As between the ADA and the FHA for an ESA (enough acronyms for you? LOL), the law would come down against the person who "came second" if you will. Using the OP's fact situation, where the four roommates have lived together, one can presume, since the beginning of the academic year, and NOW one of the four creates a conflict between one of the roommates ADA allergy, and her ESA, I believe the court would say "ESA person....you created the problem by ADDING your animal, you are the one who must move" vs. the roommate who has the allergy all along and it wasn't an issue. On the other hand, I think if a person with an allergy was to JOIN a household where an animal was already present, s/he would have no basis for insisting that the animal go. Courts will apply common sense to these situations. Now, I realize that this is a purely hypothetical situation as OP has not mentioned any allergy concerns. But, she is absolutely correct to be concerned about her daughter potentially being on the hook financially for damages caused by that animal. It's grossly unfair. If the roommate absolutely insists on bringing that dog in, she absolutely should sign any contract making her bear sole financial responsibility for damages caused by that dog. Her unwillingness to do so would be very telling, and would be reason if I were OP to move her daughter elsewhere. Yes, she might have to pay the lease out she's currently in, but I'd view that as a small price to pay to potentially be out of way larger damages caused by that animal. Animals can quickly, QUICKLY, do thousands of dollars in damages to a rental unit (as a landlord, I have sad experience with tenants who've ignored my no pets rule and brought them in anyway causing huge damages that I've paid to fix) At least in my daughter's college town there are ample subleases available for the second semester, always.