@woodynho,
"She isn't good looking"
" I started to really like her"
Congratulations either you've realised that the inside of a woman is the most attractive thing of all, all that she is and in that, actually, she's good looking on the outside as well. Until you know someone, you can't assess them, what you meant was you "weren't attracted to her physically" which is normal.
You are both young. She felt/ feels 1) safe with you but also in my opinion, you are the person "male" she leans on as she misses this ex, misses a man in her life but her heart is still there.
Until she sees you the same way as you see her, she is going to pine for her ex. Keep her laughing, give her compliments, keep your distance romantically, yet, make her feel special. Time will tell whether she then actually starts to fall for you and gives your relationship together a chance but never, ever, if she does, start to wonder about the ex, it will eat at you and you'll crush the relationship. Time.