Coworker is monitoring my FMLA use and contacting my second employer — how would you handle this?

I’m a flight attendant looking for some advice on how to handle a situation with another flight attendant.

This coworker is not a supervisor or manager; she holds the same position as I do. I’ve worked with her maybe five times in the past two years and have always been polite and professional toward her. However, she has developed a reputation among several coworkers for being difficult and for seemingly keeping tabs on other employees.

Her latest focus is FMLA. She apparently believes that too many people are using FMLA and has been trying to “catch” people she thinks are abusing it.

I have one FMLA day available to me each month, which allows me to call in without repercussions when I need to use it. Because of how our scheduling/call-in system works, my calling in generally does not leave the operation short-staffed because there are many people available to be called in.

Recently, I found out that this coworker has taken things much further with me personally. She has apparently told other employees that she called my second place of employment on a day I called off from the airline to see whether I was working there. She has also asked other coworkers to go into my other workplace and take pictures of me to see if I am there.

I find this extremely invasive and unsettling. I don't understand why someone who has the same job as me feels entitled to investigate my whereabouts or involve other coworkers in monitoring me.

There was also an incident where she was caught taking pictures of another flight attendant she doesn't like while that person was using their phone in the jump seat. We technically aren't supposed to use our phones there, although it's something employees routinely do, including this particular coworker. So it seems like she is actively looking for things she can use against people she doesn't like.

At this point, I’m torn about what to do. Part of me wants to confront her directly and tell her that I know what she's been doing and that it needs to stop. But I'm also wondering if confronting her could make the situation worse.

Would you:

Go directly to her and confront her?

Bring this to a supervisor/manager even though she isn't my supervisor?

Document everything and wait until there is more concrete evidence?

Report the fact that she contacted my second employer and asked coworkers to photograph me?

Do something else entirely?

I don't want to create unnecessary workplace drama, but I also don't feel comfortable ignoring someone actively trying to monitor me outside of work and apparently recruiting other employees to do it.

For those of you who have dealt with something similar, how would you handle this?