You shouldn't worry about what she says.
You said it yourself;
"she's pretty shallow and spoilt and pretty.. dumb"

So, what she says really has little meaning- and shouldn't affect you!
She's probably just hurt that somebody doesn't like her, and they haven't had the guts to tell her. She's trying to make you feel worse than she does. If you let her, you're sorta giving in to her; so, put on a smile! That'll confuse her.

That's my favourite thing to do. If you're "at war" with a certain person or a certain group of people, when you see them, give them the biggest smile you can! That'll annoy them more than trying to get revenge.

Also, I think you're just scared of getting too close to another person because you feel like you're gonna betray 'Ryan', or forget about him. But, i'm sure, if he made such an impact on your life, you're never gonna forget him, and nobody can ask you to. All the memories of him are yours, forever; to keep.

I'm not sure what else to say!

Good luck!
Jay x