So did she come back clean? Doing a background check on someone that you are choosing to help you in that way doesn't really sound like a terrible thing to me. You should have been upfront with her about it from the start. I don't think you have all the burden on you for the meltdown of that friendship.
Back in my drinking days one of my friends and I found a site where you could do free searches on people. We put everyone we knew in that site. Only one of our friends even came back with something and she took crap from us. She wasn't mad.