Dunno, I kinda dislike Sayo's attitude towards mc, I mean, I know she's fragile or sick and everything but c'mon, she's not a baby that needs surveillance 24/7! I got the feeling that her attitude would turn from cute to annoying in matter of days.
I get what you mean by being overbearing and I also dislike it when a partner doesn't trust the other and constantly babies them, but I don't think Sayo is being like that. If you reread, Sayo herself phsycially always gives MC space and is never overbearing with her words. It's just the arrows that are a symbol of her concern. I think worry and concern for others is normal and fine to have. It just becomes a problem when one oversteps their boundaries to act on it.
An example would be that scene where the arrow nudges her: Sayo stands behind her and the arrow is a symbol of Sayo watching to make sure she doesn't hurt herself, but Sayo is not overstepping boundaries by taking action to hold her hand at all times to help her up stairs. She's just behind MC to catch her if she falls, but she lets MC walk up her own.