Odd feeling about this girl

Reposting again because my question has changed!! So first I 100% trust my bf, we are long distance and I have known him awhile and know his intentions. Well this friend of his who I have met is very nice to me. I personally think too nice since she acts kinda fake. Anyways my bf mentioned needing to borrow a friends car to drive home (5 hour ride there and 5 hours back). Well idk why but she offered immediately when he told her. Here's my thing why is she so trusting to my bf. I personally have a leased car and would never want anyone driving it besides me, parents and my bf. I just don't get why she trusts my bf so much. Yes, he's a responsible polite guy but still. I wouldn't let my roommates bf take my car that far away for that long. Am I wrong? Should I just say kinda weird how she trusts you or should I say nothing. I am very aware of everything he does because even though I said I trust him I don't want to be blindsided by him ever cheating ( not that I believe he will but long distance and all sucks) Ik I need to talk to him but I'm not sure exactly how to start the convo without blaming him since he didn't do anything.