Well, i'm only going to mention things in pieces. I think it'll work better that way. Also, you may see some of the other admins giving their 2 cents simply because most of them have a lot of well developed characters and they may have tips of their own. Overall, you need to do as much as you can to steer your character away from doing the same thing or being too much like the standard tv or movie characters, or even like a lot of the ones here on PA. You want to make that person as different as you know how.
Please explain to me how stubbornness is a strength. I dont' get that. In most societies and cultures, stubbornness is seen as a weakness. If you see it as a strength, tell me how. Also, she's only 20. Its unlikely she would be good with a wand and with potions both. That is more the "speed" for someone who is a bit older.
I'd like her to have a stronger patronus. If you remember the books, harry's memories were really challenged until he found the one thing that was as close to bliss as he ever knew.
The Mirror of Erised is supposed to help you figure out what your character wants most. She seems a bit shallow if all she wants out of life is, really, to be a good person and to have this one person in her life. Maybe she needs to be a bit more deeply developed.
Lets start with some of those things, at least for my opinions.
k.