This was because she couldn't remember the make and model of the interviewing detective's car, wasn't it?
I don't think that makes her "unreliable". Not everyone is interested in cars. I couldn't recognise most makes or models, but I would recognise one if it was a type of car I'd driven, or was otherwise familiar with.
Ok and also add in the fact nobody else saw the car at that spot for hours after she claimed. I think she saw a completely different car and it drove off at some point that afternoon and because she has zero knowledge of cars she got confused.
IMO