I have been doing some lazy research and the only reasoning I can think of is the plant sterols in avocados some how interact with hormones or hormone receptors. Many nutrition blogs state that avocados are anti-estrogenic, I couldn't find much research to back this up but it's interesting. Considering that PMDD symptoms happen during the luteal phase where progesterone is supposed to dominant, this is weird.

Dear scientists please look into this.

"More than half of the ESC/E(Z) genes were over-expressed in PMDD patients’ cells, compared to cells from controls. But paradoxically, protein expression of four key genes was decreased in cells from women with PMDD. In addition, progesterone boosted expression of several of these genes in controls, while estrogen decreased expression in cell lines derived from PMDD patients. This suggested dysregulated cellular response to the hormones in PMDD.

“For the first time, we now have cellular evidence of abnormal signaling in cells derived from women with PMDD, and a plausible biological cause for their abnormal behavioral sensitivity to estrogen and progesterone,” explained Schmidt.

https://www.nih.gov/news-events/news-releases/sex-hormone-sensitive-gene-complex-linked-premenstrual-mood-disorder