@pamK , I'm looking at this from a T1 perspective, not sure how well that translates to a T2 position, but my take on it is that I go to my checkups, if I get advice that conflicts with what works for me, I'll sometimes discuss why we disagree, maybe sometimes I'll end up agreeing with them if they persuade me, other times not, and sometimes, I'll just nod my head, and then carry on doing what I want.
Important point to remember is that unless your sis is subject to some sort of court ruling which gives docs the power to insist what must be done, she is a free person in a free world who can do whatever she wants, including ignoring dsn advice.
A dsn cannot demand anything. I'd forget about patient's rights, it's too much hassle which will tie your sis and an overburdened NHS up in legal knots.
Instead, I'd nod my head, pay a bit of lip service to what they're saying, and then carry on doing whatever I want - if that's lc and it works for your sis, go for it.