I don't think multiple is somehow worse than single, but I read this as presenting it as a wanted pregnancy.... maybe I'm wrong.
So, if a wanted pregnancy ends up being multiple... then I personally/morally would not consider abortion an option - because I wanted to conceive a child. (Hypothetically) when I (or the woman in question) chose to try to conceive, I also accepted the possibility that it could be multiple. I could not abort a wanted pregnancy unless my health was at serious risk.
So that's my personal perspective. On to my legal/social perspective. I don't know her circumstances and it is entirely her decision.
Women also have the option of selective abortion - where 1 of a set of twins is aborted. Also something I personally could never morally do when it is a WANTED pregnancy.
If it is an UNWANTED pregnancy and I was told it was multiples I don't think it would alter my decision in any way, no.