Im not 100% but I think its she assumed since she pointed at abs the thought floated through her head that her kid was heterosexual? I keep thinking of the old simpsons where the bullies were calling the pudgy german kid gay and he was like. Im nothing yet.
I guess she’s trying to understand her daughter’s development through said daughter’s interactions with the world. Part of which is sexuality. Which it’s important for a parent to be aware of and help navigate.
If an older child expresses sexual behaviour, you have to take it seriously. That does not justify expressing sexual behaviour towards them in return, or any other creepy stuff.