my husbands child's mother...

So I have been going to the same gym located near my home. She does not live near us. She and I are also not on great terms. Cordial but not friends or nor do I like being near her. 
Well when I saw her she told me she joined this gym that my step child told her I go to. Well she started at a different location and now I find out she switched to the one near me.
Like really ? You are going to drive an extra 20 minutes to go to my gym? 
She is a very jealous woman but as the other side I don't understand why she switched when I told her which one I go to when she asked me? 
Can someone from a different perspective explain this to me? Why is she at the one down the street from me when she could go down the street from her to the exact same one?