What should a single mom with 3 kids pay in rent and a roomate to a single male friend?

My friend is going thru divorce and she is having to move. she is going to move into her male friends home (nothing sexual) and she has 3 kids. his morgage is 1000 a mth plus all utilities its a 4 bedroom house. he has no kids. she will cover food with her foodstamps as well. i do not want her ripped off but i feel he is being a lil unfair in the amount asking. she needs to make a decision fast how much should she pay??