Liabilities are endless. I'm not there, no riding. When I have someone take care of my horses when I'm gone, I don't even want them to walk into the paddock, just toss the hay over the fence please. Of course I'm usually gone only overnight or the most 2.
I'm very protective of my horses and also don't want anyone hurt. I don't like strings attached either, so I pay whoever takes care of my horses.
Have a neighbor that wanted to trade lessons for taking care of the horses one weekend, but I payed them instead. I'm not a lesson facility (don't have the time or the insurance for that).
If she's doing this with out pay, than maybe set up some time to ride before or after with her as payment.
So as far as jealousy goes, that doesn't fit into the picture with me, it's more of a liability thing with me.
Be the kind of woman that when your feet hit the floor each morning the devil says, "Oh crap, she's up!".