“Male fail” is a slang term from the trans community (at least online, not sure how widespread it is in general). It refers to when a trans woman is trying to fly under the radar by presenting as male (also known as boy-moding), but for whatever reason does not manage to pass as one and is recognized as female. Sometimes due to mannerisms, sometimes because their HRT has progressed too far, etc. This is usually seen as a good thing, since it is gender-affirming to not be seen as your assigned gender, but can also be dangerous if it leads to transphobic abuse.

In this case, the implication is that the local “Lord” has been collecting pregnant mare urine to extract feminizing hormones for ye olde HRT, and is embarrassed and happy that it is apparently working, since the peasant saw her as a lady.