\link{http://www.independent.co.uk/news/uk/home-news/court-to-rule-on-sterilisation-of-pregnant-woman-2214916.html\here's another link}
I have mixed views on this.
On the one hand perhaps it is ethically wrong to make that decision on behalf of someone else.
However, it is said that she is incapable of looking after a child, therefore if she has a child, it will presumably be taken from her (and we don't have any information as to whether she has immediate family who would be willing/able to take on any children she might have).
Essentially this woman has already been told that she will not be allowed to have children. The difference here is that if she is not sterilised, she could still carry children, then have to go through the trauma of having them taken from her at birth, assuming she has the mental capasity to even realise that's what's happening.
And what of the children? Is it right that children be allowed to be born into the world knowing that they will all have to be taken into care and potentially adopted?
Isn't it better that steps be taken for there to not be any babies in the first place? Sterilisation is permanent. Presumably her disabilities are too.
I'm not sure why administering a temporary contraception would be different really, and a temporary contraception could have other side effects.
If she is sterilised, she won't have to have follow-up appointments to ensure that her contraception is working/for it to be re-administered etc.