I unfortunately have gotten burned several times to where I now adopt the attitude that I don't loan things unless I can accept with them being a gift.

I would pursue trying to hold her accountable but it probably won't go very far. I would call the police non emergency number and maybe they can guide you. You never know.

I would also post something where ever you can (bike shop, pawn shop, etc) and offer a 'reward, no questions asked' if you really want it back.

Sorry you lost your bike. I had a similar situation. It's so frustrating. But don't give up on helping people!