Susan, as a Hufflepuff, knew where the kitchens were in the castle. She also knew that house elves worked in the kitchens. So, during one of her free periods, she left her common room and ascended the stairs until she found the painting of a pear.
She had heard of the entrance, thanks to a couple of seventh year students, who had bragged that they were the ones to show the famous Weasley twins where it was. From there, it was easy to convince them to tell her where the entrance was and how to get in.
She tickled the pear, and quickly opened the door and slipped inside. While technically, students were not supposed to be in the kitchens, in practice (according to rumors, anyway) the elves welcomed everyone with open arms and the faculty never checked in there.
When Susan entered the kitchens, she wasn't sure what to expect. What she found was surprising, even so. The elves were happily using all kinds of magic she had never seen to cook, clean, wash, and all sorts of other tasks. The room itself looked like a replica of the Great Hall, except that instead of a magical ceiling, they had only stone. They also did not have the chairs for the faculty, nor did they have the candles or main door the real Great Hall did. Instead, the area behind the staff table was filled with stoves, counters, ovens, and all other manner of cooking devices being operated by magic.
Susan stopped short as she saw the expanse of the kitchens, and that gave the elves time to notice her.
"Student guest!" shouted out one of the elves excitedly. Susan had only a few seconds to realize what was said before she was suddenly attacked.
The elves dragged her over to a table like young children, forcing her to sit. Before she had a chance to get a word out, she was sitting at a table with the elves trying to serve her lunch.
Deciding that the elves had their own form of educate, Susan decided to go along with the meal for the moment.
"What is Miss Student wanting for lunch?" one of the elves asked excitedly.
Susan, in spite of not knowing what exactly was going on, recognized this as something of a test, so she answered after some careful consideration.
"I will eat whatever it is that you and your people recommend, Mr…"
The young elf in question immediately gasped and drew back, before looking at her very closely with wide eyes.
Susan cursed herself internally. She had been in here less than a full five minutes and she had already made a mistake.
"You's is trusting elves and treatings us like equals? Who's are you?"
Susan was taken aback by the adoration she saw in the eyes of the elf. She was even more surprised when she realized that nearly twenty elves were staring at her in something akin to awe. Apparently, her social gaff was not as serious as she thought at first. Or, at least, it was not going to get her thrown out.
"My name is Susan Pevensie, I am a queen of Narnia, and I have come here to seek your aid." She said calmly. In fact, she delivered this pronouncement in the same way she once delivered announcements seeking treaties with other nations such as Archland and Calorman.
The elves went quiet at that pronouncement. Then, one of the younger female elves asked quietly "What is it yous wants us to do?"
Susan smiled kindly at the elf and said "I'm not entirely sure; you see, my siblings and I once ruled in another world, where our nation was known as Narnia. There were no house elves there, so when we returned to Earth, we decided to seek out our old allies, and some new ones."
Another elf bowed deeply as he said "We's is honored, your's majesty."
Susan then asked "Is there one among you who is the leader of your people?"
The elves drew back and started whispering among themselves. In the mean time, the elf who had originally taken her lunch order returned with a small meal.
When Susan saw the meal, she was surprised. It consisted of fresh green vegetables, a glass of pure water, and a couple of small fruits she couldn't identify. It looked like a meal a dryad might serve back in Narnia, and Susan thought about the meaning of that, even as she savored the meal, and the small taste of home.
Unfortunately, she then remembered her aunt in this world, and realized that unless she separated herself from Susan Bones, she could never go back to Narnia.
Before her thoughts could continue along the dark path they were traveling, the elves returned with an elf by the name of Doebor elected as spokes person.
Susan thanked him and the other elves for the delightful meal, and then asked to speak with Doebor directly.
Over the course of the next few hours, Susan learned about the house elves. How they were bound to their masters by an ancient spell, and how they were forced to draw their magic from the master they served. Susan was horrified by the tale, until Doebor told her that the house elves truly enjoyed cooking, cleaning, and serving, they simply did not enjoy not having a choice about who they served.
They would be perfectly happy serving a good master, but many of the wizards, they were forced to serve these days mistreated their elves. Hogwarts was the refuge for many abused or freed elves.
The elves that were freed from bondage were, in a way, even worse off than those with abusive masters. They would slowly lose their magic, go insane, and die unless they were working almost constantly in a public place.
Susan took these revelations in stride, despite her personal anger at the situation. After all, when she first met the dryads, she was horrified at the idea of being bound to a tree, but later she realized that such a thing was not a punishment at all, but instead a reward. One that virtually delivered eternal life and unearthly beauty as part of the package. She supposed that the elves felt the same way about their own situation, however much she personally abhorred the idea of slaves.
Still, the issue of an alliance with the house elves was made complicated by the fact that all elves were bound to their masters, and had to serve them first.
Susan compromised by asking the elves to help them when it did not violate their master's orders. In return, Susan and her family would try and find a way to break the slave binding portion of the ancient spell with Deep Magic.
As Susan and Doebor were ending their negotiations, a pulse of Deep Magic swept through the castle. Every magical being felt it, but few knew what it was. Susan did.
"Lucy!" she gasped. The elves looked at her with concern, so she elaborated. "That was my sister trying to wake up the trees of the forest, I've never felt her use her power so fully."
The elves smiled when they heard that. While they had agreed to help the Narnians, they were unsure whether or not the royals could keep their end of the bargain. Feeling the power wielded by one of the Narnian royals rush through the castle and themselves, they were encouraged. Those who had hesitated in supporting the deal now saw that it could work out better than they had hoped.
Susan curtsied to Doebor, robes allowed such things after all, and then left the kitchen, racing to the walls of the castle.
When she got there, she found she was not the only one; in fact, most of the school was present on the walls looking towards the forbidden forest. Susan could see why.
The trees were wakening up.