Can parasites cause burn marks on skin?

A friend of recently came back from Bali, she didn’t drink tap water but did shower in it and ate the food, she said that she felt really sick whilst over and came down with a really bad stomach cramps with all the classic symptoms of food poisioning – hugging the porcelain bowl.
She had it for a few weeks and then developed some weird burn marks on her skin, then she went to Mexico and came back with the same thing, she thinks it’s a parasite but doctor has told her it’s not fungal or bacterial, however she has massive burn marks which look as though they are peeling…. does anyone know what this is?
The second time in Mexico she didn’t get sick but she got the marks again – I think it’s a parasite but obviously I“m not a doctor and she can’t afford tests at this stage.
Thanks so much.