Of course it could be. But it could also be many different reasons.
You might ask in the right way and she might not.
If she's riding him on a regular basis, she should probably get lessons.
If she's not going to be riding him too much it probably doesn't matter.
Yea, I'm telling her the way to ask him but I think it might also be that when he went though a bad stage of riding eg: wouldn't move, buck, and do little circles. I was the one that got on him every day and tried to ride him.
Although its pretty cool being the only one able to ride him cause it means my sister can't just go running to mum when I say no you can't ride him and tell mum who then says yes. But I'm hoping to get one of my friends on him who is a very good rider to see if she can get him to behave for her.
something similar happened with a friend & I she got a 4yr old OTTB and had only been riding for about 8 months and would cry and complain about a usless a horse was if it crow hopped or got the wrong lead so I felt bad for this poor horse. We were working on just walking him over a ground pole (no real reason other than she tried and he stopped) and he stopped and she started to cry and got off him and stormed off. I hopped on him and after a little bumping he walked over fine. For her I think she was too 'emotional' and inexperienced and a bunch of other things to be working with a 4yr old OTTB. Sorry if this didn't help you, mostly just sharing I've had something similar happen.