I am sorry to hear that your little girl is showing these symptoms. Canine Hip Dysplasia (CHD) is associated with laxity in the ball and socket joint of the hip, which includes the head of the femur (ball) and acetabulum (socket). As CHD progresses, the laxity of the hip joint, leads to loss of cartilage, bone spurs (osteophytes) and scar tissue as well as progressive loss of muscle tone in the hind legs. The causes of CHD are multifactorial. Genetic predisposition is the main culprit but rapid weight gain or rapid growth as a puppy can further predispose a patient.
Symptoms of CHD are limping, inability to jump, muscle loss and hip pain. Young dogs such as your girl, who show signs of hip laxity will likely go on to develop further symptoms and eventual painful hip arthritis. For this reason young dogs showing symptoms should be given a full orthopaedic evaluation, including X-rays to determine the severity of the condition and confirm that CHD is the sole cause of her symptoms.
It sounds like you have been applying most of the medical treatments recommended such as weight management, low impact exercise (walking, swimming) and anti-inflammatories. Younger dogs tend to not respond to medical management as well as older dogs and surgical intervention is therefore recommended. In addition early surgical intervention can help to prevent the devastating progression of the disease. There are several surgical options, these include triple pelvic osteotomy (TPO), total hip replacement or femoral head osteotomy. TPO is usually only appropriate for young dogs not yet showing signs of arthritis.
I can understand your concern after seeing your girl suffer from episodes of hip laxity. The good news is that there are excellent treatments available but I would strongly recommend a full orthopaedic workup and referral to a veterinary orthopaedic surgeon if necessary for assessment of her suitability for surgery.
Best of luck!