Hi, my dh as got a sis who is 16 recently she has been talking to me frequently and asked me if i would go with her to go on the pill, because she doesn't want to tell her mum, also to get condoms for her. I feel i should so i know she is safe, but also don't want family to feel that i am going behind there backs??
I'd take her, to be honest; at least she's being sensible enough to keep herself safe, and feels that there's someone she can talk to about it. I did the same thing for my little sister when she was 17 and kept it secret from my parents.
I think you're making too much out of this. She is over the age of consent, and she could go and see the GP on her own if she wanted to, so you are not going behind anyone's back. And no-one need ever know that you took her if you don't want them to.
If you can't handle it, then don't do it. You shouldn't feel pressurised into doing something for her that you don't feel comfortable with. If you're comfortable with it then I can't see the problem.
And bear in mind that if you go behind your SIL's back and tell her mother when she has asked you not to, you will have betrayed her confidence badly, and you will never get it back. Telling her mother that she's on the pill/sexually active is her decision to make, not yours.