I’m guessing that a good conversation is in order – one that doesn’t condescend to her or put her on the defensive, and one that expresses concern about her well-being more than irritation at her immaturity. Say that you see patterns of self-sabotage. Then offer your help in averting some of these mishaps, after asking her if she really wants your opinion. When you’ve respected her enough to have this dialogue, if nothing changes, then you get to decide whether for your own sanity you need to build in some distance.
Might she be scared she won’t seem as attractive to you anymore? Frustrated with the time or money now spent on your appearance that wasn’t spent before? Jealous that you’re becoming more attractive than she is? Worried that there are – or will be – other personality changes that go along with the changes in your pecs? Yes, I get it, you’re feeling great. But when your partner’s not, no matter what the reasons, it’s up to you to work on it.