Ever since she had returned, Rose has spent most nights on the TARDIS curled up in the library reading and most of the time studying. If she asked herself, it is really just what she wants to do with her time, which is a far cry from the Rose Tyler that she had been almost five years ago.
That Rose Tyler was a frustrated working-class girl who was looking for an answer that she eventually found in meeting the Doctor. When the Doctor filled the void of what she looked for in life, she realized quickly that she was fast falling for him. She fell for an alien that was different than anything she had ever witnessed in her life and loved every minute of it. Rose Tyler was young and even idolized her Doctor because he truly was her everything and she was willing to do everything, but lose that. She wasn't so lucky in that respect, because just as soon as she found peace she had lost her life.
In that parallel world, Rose changed. Gone were hopes and dreams of a blissful future, and she was met with a harsh reality of wanting to live a flashback. Ask anyone she talked to, including her mum, back then and they'd tell you that they couldn't see her pain because she hid it well. They would have told you she was happy and moving on, but only the Doctor could understand that. Being reunited with the Doctor proposed a question on where her life would forever lead, and she had chosen to once again make that flashback her reality. Unfortunately, the flashback had a whole lot more color in it from what she remembered.
When Martha was in the TARDIS, the problem had been masked. Rose could explain that things weren't as they were because Martha was on board and with them. As soon as Martha went so did the excuses, and thus, this night being right after the event, is a particularly hard one for her. She isn't studying tonight; she's just staring at her book.
Rose still loves the Doctor, but she can never claim him. Back on that beach, so long ago, she had confessed her love to him only to have never heard back. Six months have passed since she was reunited with him and an answer still remains. Rose hasn't directly brought it up because of the sore subject it might be. What if all the signs were misinterpreted and the only love back was for the friends that they were? When the Doctor chose to save Rose in the dungeon at that castle maybe he was making a unilateral decision. The Doctor seemed to have held more trust in Martha than her and now was keeping more things from her knowledge than he used to. Exactly what did he see in the student's memories that made him look at her with worry and not even address it when she asked?
Plain and simple, the Doctor treats her like the child she was when she first met him. Back then with him as her idol, she couldn't see these things and masked all doubts with hopes. Now, she sees the holes and has found reasons to regret. The family that she loved and was sure loved her back is nothing but a distant memory. All she has left are uncertainties and a dying since of hope. It's the main reason why she never introduces herself with a last name anymore.
Of course, don't get Rose wrong. She now is happy, genuinely happy to be in the TARDIS. She loves this sentient time ship and it loves her back. She loves the adventures and even when they seem dangerous and grim, they love her back too. It's wonderful and it's great, and the running never tires Rose. She can run forever and unless she meets a cliff on a journey, she might just do that!
Yup, that is Rose. Running from her problems and enjoying her present and hopeful future. In that respect, Rose has never changed, nor ever will, from the Rose Tyler she used to be.