@kitation hi, I have a few thoughts...
If you're not aware, there's a process for complaining about NHS services https://www.england.nhs.uk/contact-us/feedback-and-complaints/complaint/
If over the counter painkillers are not sufficient to manage the pain, and she hasn't been offered something a bit stronger, then the GP is not doing their job IMO.
ME/CFS has many co-morbid conditions that are treatable and should be investigated. See e.g. https://batemanhornecenter.org/education/me-cfs/