Legal Question in Criminal Law in Florida

You can pay your girlfriend. The motorcycle is in her name and thus she is the lawful owner. This is no different than any other type of gift. If a boyfriend buys a gift fr their girlfriend and they break up, the gift belongs to the giftee, not the gifter. The fact that you paid for it simply establishes that you got her the gift. Unfortunately you can't stop her from doing what she wants with her property.

I wouldn't really say this is a criminal law question, but let me offer a different perspective. I'm not so sure that I would call this "her property". I think it may be possible to sue her, but it will require some proof that this was NOT a gift. Just because the bike is titled in her name doesn't necessarily mean it belongs to her. You could hire an attorney to get a declatory judgement, or even a remedy such as specific performance, but again it comes back to proof. Can you prove that this was yours and not hers. Your brother could file an affidavit, but that will require you to file suit. If this seems complicated, it's because it is and that is why you need an attorney.