AITA for refusing to cover my coworker's shift for the third time this month?

I (28) work retail with a coworker, "Jen" (30). She's asked me to cover her shifts three times this month — always last minute, always with a different excuse (dentist, her car broke down, her dog was sick). I said yes the first two times because I felt bad, even though it meant rearranging my own plans.

This week she asked again, texting me an hour before her shift started. I said no, because I already had plans and honestly felt like I was being taken advantage of. She had to call our manager to find last-minute coverage, and now she's telling other coworkers I "left her hanging" and wasn't being a team player.

Some of my coworkers think I should've just helped her out since she's covered for people before (never for me though). Others think three times in a month with no reciprocation is more than enough and I don't owe her anything.

AITA for finally saying no?