Well it happened.
You're right they wouldn't have accepted the results. They called her while she was taking the pregnancy test to tell her not to bother, because it wouldn't be accurate enough anyway.
She was going to fight them on it, but the test was positive. So she just came home instead.
Her regular doctor said she wasn't going to recommend that facility anymore, because the whole thing is fucked up regardless of the outcome.
Even though mammograms are generally considered safe during pregnancy, her doctor just did an ultrasound instead. I believe that's because the doctor wasn't that worried about the lump, otherwise she'd have gotten the mammogram.
I didn't mention all that other stuff in my original comment because I don't want to distract from how fucked up it is that they treated her that way. It doesn't matter whether she was actually pregnant, or even if mammograms are considered unsafe for pregnant women (and again, they're generally not). They put a hypothetical unborn child over my wife's health. It's unacceptable.
Fiction.
My book store would not have a lot of sections.