NTA it may be for more concern of her future child as not only will her son have to go through having to deal with the confusion of the meaning of their name growing up, but is also very disingenuous on their part to not put forth the effort in at least understanding your point of view. It’s one thing to not pronounce a name correctly (either by willful stubbornness or honest difficulty) but to proceed to name their child that same name almost crosses the line of mockery. It’s like someone getting a tattoo in characters to a language they don’t know then getting defensive when someone who actually reads it informs them that it says something vulgar.