You said the problems started just "late into day one"
Sounds like something other than the fast has caused her problems.
Something previously eaten? Possibly an ulcer?
Not really sure. But if she was having problems the same day she started the fast, thats kind of quick to already have issues that are not directly correlated with fasting detox.
I'd suggest seeing a doctor as well if the pain continues. If she does start a juice fast, drink low acidic juices.