“Systematic reviews of controlled clinical studies of treatments used by chiropractors have found no evidence that chiropractic manipulation is effective, with the possible exception of treatment for back pain.[8] A 2011 critical evaluation of 45 systematic reviews concluded that the data included in the study “fail[ed] to demonstrate convincingly that spinal manipulation is an effective intervention for any condition.”[10] Spinal manipulation may be cost-effective for sub-acute or chronic low back pain, but the results for acute low back pain were insufficient.[11] No compelling evidence exists to indicate that maintenance chiropractic care adequately prevents symptoms or diseases.[12]”
Honestly, your girlfriend would be far, far better off going to a competent physical therapist. It sounds like there’s a muscular weakness that’s allowing a joint to not stay in place.
In almost all cases, people will get better long-term results by doing physical therapy rather than going to a chiropractor.