"She has three credits to pay for her house."
Translation:Elle a trois crédits pour payer sa maison.
"Elle a trois crédits" means she has contracted loans from 3 different sources
Loans or mortgages, yes. This is one of those "Report a problem to duolingo" situations
"Credits" is not acceptable English here. (Except perhaps if you're in a science fiction movie, and the cost of the house is three credits.)