My boa's have never gotten into their bowl unless it was to poop in them. I don't see why it would be bad though. Just like some BPs like to soak, some boa's do too. As long as it isn't a deep bowl she should be fine.

Boas do like it a bit cooler than BPs so if yours does spend time soaking, I would check for signs of mites, and to be sure it isn't too hot in the enclosure.