I don't remember ever reading that at all about Penny.
However their scenes evolves, there is a significant difference though.
for the confirmed virgins, MC has to build up to it and make the first moves before it actually happens. getting them in the mood and convince them to cross the line, even if they actually want it all along. they have to be "ready".
Penny and Alex, they are clearly different. they were driven by lust and initiated it themselves, even convinced themselves and made up their mind on their own, as if they already knew what sex feels like and they missed it. similarly to Nancy. they just go even further because of how good it feels with MC.
Penny going full sub probably because of her true kink and fantasies that she began having after experiencing sex, but waited to have the right partner to be able to.
He didn't fuck the shit out of Dalia. She fucked him for 90% of the scene, and he just finished it when she was exhausted
for the confirmed virgins, it was very explicitly detailed that they were virgins and MC is their first. So if I think it's not explicit for some girls, then it just means they were not virgins, and Caribdis just wanted to avoid the Anti-NTR brigade by avoiding the subject for those girls
actually red hair is a recessive gene

so if their dad had black, dark or brown hair, they would have a high chance to not be red heads. Penny being blonde tells us that the dad had one gene for dark hair and one gene for blonde hair.