It takes her too long to realise she is pregnant. (She supposes, in the end, it shouldn't surprise her.) She doesn't know who the father is (one of the men in the church), but she takes it to their leader anyway (what else is she supposed to do? They'd notice eventually). His reaction is almost predictable. She doesn't expect his vehement opposition to her child even truly being a person. She can't stand the idea of them hurting her child (they are good, even now, before they're born she knows that, not like her, she deserves everything), if they even let her keep it (she knows they don't agree with that, not normally, but...but he had said her child was nothing more than a parasite).

She is dismissed with only minimal punishment. (It might be her fault for tempting the men, but he seems distracted.)

She can't stay here. She knows that. Not with the child growing inside her, it's too much of a risk. So, she does something she never would've thought herself capable of. She takes what little she can carry, and runs. (And if the church catches fire as she slips out in the middle of the night, she tries not to feel bad that she can't control it, that she's damned and dangerous, but she needs her child to be safe.)

Trying to survive out on the streets is...not easy. Begging gets her very little, and she's not brave enough to try stealing (she can't risk getting caught). She manages to keep herself alive, but... She knows she needs more information on pregnancy, and knows she needs more food than she's getting. (And if there's a few more fires in abandoned buildings, or in alleys, she's always cleared out well before anyone can find her, what little control she has keeps getting shakier.)

It leaves few options. She doesn't want to do this, but she knows she can (it's not like people haven't made assumptions already). And she needs to be able to stay alive, if only so her child makes it. (She doesn't have a choice.)