When I'm trying to move my paint into lope (squeeze with inner leg more in, outer leg little behind) when it's TIME for it (after 30 mins at least of work) she gives a good buck and sometime moves into pretty nice lope or sometime refuses to go into lope and just keep trotting. Saddle does NOT hurt her. She tries to canter from trot when she's fresh (first 10 mins or so of trotting) and cantering with saddle (and me ) certainly doesn't irritate her. I have a feeling that she's tired by the time I want to lope, and just don't want to do it (she also pins her ears somewhat when asked). She's still young too (passed 4 years old). How to deal with this buck and refusal to canter? Can be the reason for the buck that she tries to balance herself (that's what mom is saying when watching me)?
BTW, she's very quiet on lunge (not like my other one).