What other aspects of play are you considering here? It's the beginning of the game.
I'll give my interpretation here. Given Flower's sequence of actions:
- Agreeing with your accusation that she was nervous
- Saying she has something she wants to discuss but is waiting until everyone has arrived (which was unclear at first, but now checks out as waiting for her mason to get here)
- Couldn't abide by her own deadline and bursts forth with what's on her mind immediately and in public.
I think all of these fit the profile of her being townie. I think as scum, the default assumption is that she tries to sooth her masonry partner in private and keeps a lid on her role at least for now. For her to be scum here requires quite a bit of performance and self awareness.
You could argue she claimed just for the sake of credit but then she immediately discredits the reliability of her own claim with her questioning whether or not to say anything about her other mason.
So I think she's more likely to be town.