She dumped you, I suspect because she wanted to explore being single on her own terms.  But, at infrequent, lonely times,  she isn't sure she made the right choice.  Retaining this items allows her to have a justification to reach out to you in person at some indeterminate time in the future of her choosing to see if she made the right decision or if things fall apart for her as she runs around pursuing other romantic issues.  What she hopes for, is that she can keep you on the side burner pining away for her and she can come back to you as a fall back.  Symbolically, her giving these items back would mean you've really moved on and its over, which it probably is anyway, but she needs to be sure.

These trinkets you worry about?  Are they worth more than your pride and sense of self worth?  Let them go, friend.  It's time to move forward with your life free of her machinations.  You control your destiny, not her.