The mare is N/H however I think contacting the owner would be a good idea to get more info before thinking the worst. I also understand that you just never know. I've talked to her about the mare and she hasn't mentioned anything about a special diet and she also hasn't mentioned if the mare has had any episodes. The owner seems pretty honest and straight forward so I think this mare would be fine. However, I wouldn't use her for breeding.
Be kinder than necessary, for everyone you meet is fighting some kind of battle.