Thanks for all of the replies guys!
I have no fear of her "messing him up." We're not top level competition by any means
I talked to her and she said she knows he's my baby and would feel bad, but I told her it would be okay. I gave her my number and told her to shoot me a text when she was looking to ride him and if I wasn't going out to the barn or didn't mind hacking another horse she was welcome to it. She doesn't ride much and she'd always ask first, so I'm not concerned
I'm not saying she can ride him anytime she wants, but as long as it's not very often it would be good for us to switch up. Lol, I started to feel bad that she felt bad so I was like "Oh no, I don't mind at all, anytime you want, blah blah" lol! But she'll always ask first and it won't be often, she knows I love him to death - I trust her, she's basically the sweetest lady at the barn. It'll be ok!
I still don't particularly like sharing (He's MINE
), but I think this can be an exception. I've had him for five years and counting, he's not going to forget his mommy.