She should have the ability to gait. She has unlearned it. If she does a flat walk she just needs muscle memory built. The best thing for her is hills, lots of up and down hills. That is the best way to get her rear and shoulders built the up the way they should be. Another thing is spacing boards, there are others on here who can tell you how far apart to put them. Get her shod in the front and put weights on her legs, and no I don't mean anything inhumane, there are weights that are not made of chain, they are padded weights which go around the legs that will make her notice her front feet more. A trotty horse is much easier to get to gait than a pacey one.
The KMSHA rules state the horse must be certified by the age of 4. But if you talk to them and tell them the circumstances they may go ahead because of her parents, but you must have her in gait and send them a video of her doing it so I would get the training started asap.
I guess I should have read your full post too. You will know a gait when you feel it. You will feel the impulsion from the rear. She will drop her hind end ever so little and start making that back end push the front end. It may be a bit bumpy at first, but your bottom will not leave the saddle like a trot, eventually when you get good muscle tone the bumpy should go away.