More often than not, the culprit of chronic patella dislocations is a weak VMO. It's the little tear drop shaped muscle that sits above the patella medially. It is part of the Quadriceps muscle and plays a very important role in patella tracking, aka how the knee cap moves up and down. Sometimes if its weak enough, you won't even see it present in some athletes, more commonly in females. It's important to remember that everything around the effected joint plays a role. My kids always ask me why for an ankle injury they are doing hip and knee exercises as well, and I explain to them that they are all related in the kinetic chain. They found it fascinating that weak hips could be the reason for their chronic ankle instability.
It's important to focus on strength and flexibility when it comes to rehabbing the area. So for her knee, make sure she is stretching everything around the joint- calves, hamstrings, quads and hip flexors, IT band, piriformis, and even the back. the foam roller will be her best friend. It hurts so good but it does the trick. Balance exercises are good for stability. I'm sure you have some sort of unstable surface for her to work with. I honestly get creative at the school because I don't have that many resources. Start her with single leg balance stuff on the ground, and as that gets easy, progress to something a little bit more wobbly, a coach cushion for example. I try and make my balance exercises sport specific, for example with my soccer players I'll have them head the ball to me while they do it or kick/knee the ball on their opposite leg. As far as strengthening, alot of athletes get this misconception that they need to power lift a crap ton of weight. I tell my athletes start with body weight exercises and go from there. They are more often than not surprised to find themselves sore after the most basic rehab exercises. I focus alot on the hips when doing knee rehab/strengthening. Some of my favorites include ball squeezes, clams, hip haters, single leg cup stacks, whale tails, monster walks, and creek crossers. I just use a theraband, change the color for difficulty based on their progress. I'll try my best to explain them. Side lying clams- lay on your side, knees bent on top of each other. you bring the knee on top up, like a clam opening, hence the name. ball squeezes you simply put a ball in between their legs while laying down, legs bent with feet on the table. tell them to squeeze the ball in, then relax without dropping the ball. Once that's too easy I move to the wall and have them do wall sits and squeeze, and then add a ball behind the back while doing wall sits to increase difficulty. hip haters... my kids LOVE these and by love I mean despise lol you do them side lying, and you bring the top leg up (like a straight leg raise except you are on your side), back in hip extension, then forward, and back down. make sure they are keeping their body/hips in alignment and not letting them sink back or slouch forward when they do them. When those get easy enough I normally add ankle weights, or make them do them in a side plank, that way you get the core too. Single leg cup stacks is pretty self explanatory, you have them stand on the "bad" leg, and pyramid stack cups, standing far enough back that they have to reach into it. Once that gets easy, I have them move to a more unstable surface and/or do squats in between each cup. Whale tails, sounds silly I know. This may be harder to find a surface to do them on at home, but I have them lay on their belly on the treatment table with their lower body hanging off the table. They then bring their legs up and out an back down. This one is hard to explain lol but it works the glutes really well. Monster walks, you can do without a band for starters, but you put the band around their legs right above the knee cap and then they do walking squats, if that makes sense. Creek crossers you move the band down around the ankle, and have them walk and as they walk they go up and out. Some other exercises I do for knees are single leg calf raise step ups-I have them step up on the plyo box, do a calf raise, and come down. once that gets too easy I add weight, ramp squats- get them in an incline position/heels up. I normally do this on my ramp board against the wall so they can control their movement. It's a great eccentric exercise. Squats are a biggie in activating the VMO, so any squat variation will be beneficial, so long as they have good form. Hamstring bridges- They are much similar to a regular bridge you do to stretch your back, but you do it without your arms so its all in the hamstrings. have them lay down, legs bent, feet on the table, then bring the butt up, hold for a second or two, and relax. once that gets too easy, you can add a ball between the legs, have them kick a single leg out, or use a physio ball and put their feet on it and have them pull the ball in toward them.
Okay, sorry, I just get really excited about these things lol I know it's very long winded and you probably won't even read it all, but I figured I would put my 2 cents in :)