Come up with something for me to cheer up a girl who I upset and depressed, who thinks I am not trustworthy, and who thinks I don't care about her.

No, I'm not kidding. Don't ask questions, just do it. D<

Well you can't go past presents. Chocolates and flowers are good. or other random acts of kindness.

You should first try to apologize, then show her you can be trustworthy, tell her than you can prove to her that you can be trusted.