I feel like it doesn't matter if Toriels behavior can be considered whorish or not. That's just pointless semantics, no matter if she even fucked Sans or not.

But what matter is the change of perception from the in-game characters themselves.
Susie, who might as well be considered a protagonist, used to harbor a lot of respect for Toriel. Until now. Whore or not, Susie definitely now views her as one, at least until those sore feelings of disappointment wear off. And that's what actually matters. Not the "can women have fun or not" bullshit