If he is outside of the US, can she articulate the wedding plans in more detail? Has she looked into immigration law and things like that? Does she have a passport? Have they met? If not, how does she intend on meeting him? Which country are they going to get married in - and will the marriage be legal both places? I mean, I met my spouse over the internet (non-scammy) and the details really are somewhat of a pain, but was worth it for us... and we met a few times before marriage.
The gist being more that thinking realistically might help snap her out of it some.
If she comes around, are there laws that help victims of scammers that would allow for things like debt relief?