Either she played FPSs before meeting her partner or she started after meeting her partner. If after, I would wager that the husband/other party in the relationship also plays FPSs, and I'm going to make that assumption while I stand on my soapbox here.

A healthy relationship involves both parties making an effort to learn, understand, and attempt participation in the other's interests.

I can't find statistics on what percent of all women play FPSs, but most people would concur that a random women you meet is less likely to play FPSs than a random man you meet. Perhaps they are in a relationship because they shared a common interest before meeting, but perhaps they share a common interest because they are in a relationship. So let's talk about the more likely scenario for the women you mentioned: she took interest in FPSs because of her relationship. This seems to be echoed by anecdotes in some other comments.

Gender norms have created some imbalance in this regard, where the wife is more likely to make a considerable effort to take interest in their husband's hobbies.

In the classic troupe, the wife goes from being uninterested in football to learning about and watching football with her husband. If she didn't, she would miss out on spending time with her husband since watching football consumes a lot of their mutual free time. However, this effort is not always reciprocated, leading the wife to give up on her hobbies in order to prioritize time spent together.

If you want to be investigative, ask the husbands which of their wife's hobbies they've taken up. If it's a strong relationship, I would suspect they have equally invested into the relationship.