Yeah, its not rocket science. My ex needed a vibrator to cum every time. She still greatly preferred for me to be using it on her and be buried inside her when I did it. Other than a G-spot (which is not sensitive until most women hit their sexual prime around 35) the main erogenous zone is the clit, which in case no one noticed, it pretty hard to get with a simply penetration.MC needs to learn to lose his pride and work that clit while he's fucking her it's hard for many girls to come with just penetration it's not that uncommon. -shrug-
Eh, its a fantasy though. Bigger (to the point of absurdity) is better and harder is more pleasurable.