Yes, the PMT (PMS) can get much worse as the peri-menopause progresses. But PMT is a pretty sure sign of estrogen dominence, so that only makes sense. She is producing less and less progesterone as she gets closer to menopause, so it makes sense that the PMT will get worse.

It got so bad for me that if I don't take various precautions against estrogen dominence (progesterone cream, and avoiding foods that contain estrogen or estrogenic compounds), I experience extremely severe PMS all month long.

I don't know how you might bring the subject up with her, but you might consider telling her you found something that some women have found helps them feel better when they're having PMT, and not mention the menopause thing at all.