Does she get plenty of turnout? Is she good on the ground? What do you feed her? How old is she? What did she do before you?
There is nothing wrong with being a novice and asking for help and I actually think you have been quite brave to do this for 3 years and still love her! I am probably more experienced than you and would have given up by now!
There is probably lots of reasons she is doing it. You need to go back to basics with her.
Firstly I would look at her daily routine. If she has a bucket feed only feed fibre. No pony nuts or mixes. Ask in the feed shop for something like fastfibre, the lowest one for horses that are at rest. You feed it slightly soaked. And some graze on or ready grass. Or some high fibre nuts and ready grass. Just this for now so she is getting a bucket feed. Plenty of hay.
Then if possible out all day. With company.
Then either ask someone who will know what type of bit she has in. If she is dipping her head I expect it's some kind of pelham. Do the cheek pieces fasten to a little ring on the bit then the reins to a different one? Or I wonder if it's some kind of gag?
I won't advise on your bit as I haven't seen her or her mouth confirmation but definitely ask your instructer.
Is she polite on the ground? Does she tank in a headcollar or.pull you about at all? I suspect not which is why you love her still lol. If she does then look at some of the training halters like a dually. Ask someone to show you how to use it and get manners established on the ground.
She doesn't sound like she is bolting proper. She just sounds hot. Which if you have coped with for 3 years you might be able to get some manners established and work with her. She will possibly always be hot but she needs to learn not to tank you around. Definitely, definitely get a good instructer to come and help you.
Fwiw the best horses I have had have all been hot and required a certain way of riding and management. But when I was younger and braver I didn't enjoy riding a sedate cob I wanted fizzy and responsive. But you have to be able to control that energy.
Get some help and if you have done 3 years I bet in 6 monthe you are happily hacking out and everyone is jealous of her.