So I don't mean precisely that she swears, because Maeve made up these angry words, but they're words that the shouts or interjects when she's upset, so she uses them like a person would use a swear word. And I've thought it through pretty thoroughly, I don't think any of them sound like any adult interjections.
When mildly upset, Maeve utters a frustrated cry of Han Solo! This is kind of hilarious. We are Star Wars people around here, and I think she remembers that Han Solo is friends with Chewy and flies the Millennium Falcon. But when just slightly unhappy, Maeve stomps her foot and calls on the Guy Stuck in Carbonite.
Now, when the child is very angry, you can always tell, because she bellows: BEE-OPHUS! It's almost always accompanied angry screams, and comes in the middle of a full blown tantrum, or to alert us that one is on its way. The emphasis is definitely on the BEE and the OH - try shouting it sometime, and you'll find it's a pretty good faux swear.
I kind of like that she's invented her own language for when she's angry, and I don't every chide her for using her words. Words, after all, are always better than, say, hitting or kicking, which we sometimes have a problem with. And I appreciate any effort she makes to deal with her angry feelings, which we seem to deal with at least once a day. But here's hoping for a more Han Solo kind of day than a Beeophus one.