hi, she needs to go through the NHS complaints procedure first, which will give her a good idea of whether she would be successful or not (for free). If not, she would have to go directly to a solicitor, which could be costly and useless, if indeed the side effects were all to be anticipated. Yu cant use the complaints procedure and a solictor at the same time but you can go to law after the NHS has incestigated.
What makes you think these side effects are the product of a mistake? are you a surgeon?
anyway, if she is going to use the NHS complaints system, she needs to start things fast - you need to do things within 6 months of the event, or 6 months of becoming aware there was a problem (as long as its not more than 12 months since the event)
As i said, they will investigate and the report should give your friend an idea about how successful she is likely to be in suing them. if she is not happy with the outcome of the investigation, she can go to the healthcare commission to independently review it.
From what you are saying, it sounds like she would be unsuccessful, as she was appraised of what the outcome could be, yet still chose to go ahead, although if there was negligence, then of course it should be investigated and compensated