Well if that were the case she only starts Liking the MC as a man when he gets the fuck out of the house and starts adventuring instead of running the bakery and being a slacker around the slums.
Nomoshing is a Smart dude, replaying the game you only get context to their relationships when it is necessary and not before or after, and the information is precise not too much but just enough to satisfy the players curiosity or keep him distracted (like in Florine's case) ... There is a strong possibility we will learn more about the past relationship between Shally an Meline and MC/Hero-Baker. .. ... we might even get a threesome where Meline and the MC pretend they are Overpowering their Babysitter and fucking her senseless.
Also both Quotes you pointed out do make her seem like a gold digger but I also get your point there is More to her than she shows us, Like how surprised Hero Baker was when she turns out to be an agent for the Queen and Shally also shows feelings of kindness and compassion in relation to the green haired gunslinger girl during her questline, so it is hinted Shally is definitely not a shallow gold digger type. But she does want to keep seeming that way around Hero Baker cause maybe she would that way have an excuse to keep some distance between herself and him.