The judgement is very sensitive
It discusses the risk to her life from a further pregnancy; her inability to grasp the concept of contraception and the basics of reproduction; her other severe health issues including protracted fitting; and the fact that sterilisation will mean less intervention in her life from other agencies, which she finds objectionable. For example, use of contraceptive injections would mean ongoing medical intervention.
I get very twitchy about this type of intervention and I do think it's sad but in this case, I think it was the right decision. It will allow her to continue a full life with her partner without the massive risks she takes from a pregnancy, risks which she is not able to understand and mitigate in any way.
It also mentions that she most likely suffered from childhood sexual abuse, which is truly awful, but she does seem to be in a committed and long term relationship now which is I hope a happy one for her.