Glute Medius Strengthening to Prevent Knee Pain in Squats

My physical therapist told me that my knee valgus during squats is caused by weak glute medius muscles. Essentially my knees are caving in because my hips cannot stabilize the femur. This is causing a lot of pain on the inside of my knee joint.

I have started doing lateral band walks and monster walks before every leg day. Are there any other exercises that are even more effective for isolating the glute med? I have heard that side lying hip abductions and clamshells are good but they feel a bit too easy.

I really want to fix my squat technique so I can stop hurting my knees. If you have any cues or drills that helped you keep your knees out under heavy load I would love to hear them. I am tired of having to deal with this nagging inflammation.