Maybe the term butterface originated from America, but I can tell you that ''she's butters'' is a very British expression. I've heard it millions of times already. (Especially in and around London!) It was a real trendy word about seven years ago.
I wonder which part of London this was mostly used in, because I've lived in London for most of the past 20 years, and I know a lot of (mainly South) London slang, but I've never heard anyone say it.
Then again, it was probably a word which only schoolchildren used, like "nang", haha.
If we were talking about an ugly girl, we'd just say "na she ain't buff" lol :D