"How is it stupid?" Buffy asked.
"Buffy, it's the clueless about the supernatural that die because of it! If your mother can't identify a vampire on sight, like Willow couldn't, then she could be tricked into inviting one in. Xander was trying to keep the Wesen a secret, but by extension the vampires ended up being a secret too. If you mother doesn't know to take precautions after dark, like wearing a cross or carrying Holy Water or even Mace, then a vampire could snatch her off the street. And let's not forget that you're the Slayer!"
"But it's exactly because I'm the Slayer that it's safer for her not to know." Buffy protested.
"How?! How in the name of any god is that safer for her?! If anything it makes her more vulnerable. You remember Xander said how some Wesen like to test themselves against Grimm? I'm sure there are vampires that like to test themselves against Slayers and what's to stop them, once they know that you're the Slayer, from studying you? Learning where you're vulnerable and exploiting the vulnerability? If your mother can't protect herself, then it's not a stretch to think about how easy it is for a vampire to get to her and use her or worse, turn her! Especially in Sunnydale. Buffy, this town is a mecca for them. Rory Harris has been dealing with them since he was a teenager and his mother before him dealt with them too. Leaving your mother in the dark over vampires doesn't keep her safe, it's inviting ugly death to come and play with her!"
Buffy could only stare, speechless as she realized Cordelia was right, there was absolutely no logic in not telling her mother the truth.
"I actually did try telling her, back when it first started, even though Merrick told me not to. But after he died and I realized my sneaking out to find vampires was causing problems with them and they were arguing a lot more because of me, I tried telling them."
"What happened?" Cordelia asked, noting the sad and pained look on Buffy's face.
"They decided that, in addition to setting the fire in the gym to destroy the vampires that invaded the dance and running away afterwards and getting kicked out of school, it all meant I was having a breakdown and they hospitalized me for treatment. Not long after I got out, they got a divorce."
"You had no one to help you tell them, to explain it to them. If your Watcher, this Merrick dude, had helped you do that, your parents could both be helping you deal with all of this. Most Wesen don't woge for the first time until they're a little older, usually around when puberty starts. And woging accidentally can happen when you're stressed or emotional in any way, which puberty already is. We have our families to help us deal with it and learn to control it. Most Grimms grow up knowing their heritage and are trained from a young age. Xander wasn't because his father is angry and bitter that he didn't activate at all. In the case of Grimms though, they can activate all the way up to about age forty. Activating as a teenager is rather rare. But the Harris' choose to live in Sunnydale and look after the Wesen that have also chosen to live here. Early exposure to Wesen and the supernatural can make them activate earlier. Given Sunnydale is a mecca for vampires, it's no wonder that both Xander and Uncle Rory activated as teenagers. Grimm get stronger the longer they're active and to survive this town they have to be very strong, so the extra time helps with that."
"And Grimms outlive Slayers, often by years. Xander said that when he introduced himself to Giles, because they have actual support. They don't fight alone or have to deal with the emotional fallout alone, like a Slayer does."
"Buffy, telling your mother should be your choice, not Giles' or his Council's. We can help you tell her. I could woge for her, for your sake I'm willing to do that. Uncle Rory can help confirm we're telling the truth, heck there are adult Wesen in Sunnydale in positions of authority that can help us, help you tell her. You don't need to be alone, for any of it. Once we prove to her that Wesen exist, then it's not such a stretch to getting her to understand that vampires exist too."
"You guys would really do that for me?"
"It's what friends do for each other. And I think we're at least on our way to being friends, not just occasional allies."
"Who's going to help me tell Giles? Because I should tell him I want to tell my mother the truth and I really don't think it'll go over well with him, at all."
"We'll help with that too. No matter what he and his Council think they have no right to control you or tell you what to do or how to live your life. Their stated purpose is to support you, as the Slayer. Let them prove it."