Women are only fertile for a VERY short period of time one day in the average 28 day cycle. It's really only a few HOURS each month. Estrogen doesn't necessary drive her to be excessively horny either. Most women are unaware when they ovulate because the symptoms are so few.
I'm not extra interested in sex during my fertility window. A few years ago I wanted to track my fertility and found that my sex drive did not increase. Some friends also tracked theirs and none of us ever tracked higher sex drives during our fertile times. None. One of my friends was even sex-repulsed!
Estrogen is not the hormone that is often linked to a higher sex drive. It's why a lot of older women who have gone through menopause and have a naturally lower estrogen are more inclined to be sexually interested.
The fertile window of a woman does many things, including causing her cervix to lower and come closer to her opening to help sperm enter.
Many women feel like having their cervix bumped hurts. This can be a time where sex is more painful. The cervix isn't really linked to pleasure.
What likely happened is that the woman probably is looking for fun. She is probably on the rebound from a failed relationship (assuming by age) and wants to have fun again like she did when she was a teen. She has fond memories of sneaking around or experimenting for the first times with this fellow so she thought it was worth a shot to kind of relive that excitement again.
This doesn't have anything to do with where she is in her cycle. Humans aren't driven entirely by hormonal fluctuations. When we're talking about hormones that create a higher sex drive then generally we're talking about testosterone.
It was dumb he refuses to be a booty call but then decides he'll entertain her anyway with a night out. Please. Guy is horny too, and maybe has hopes it'll be more than a one night stand.