Right. My bet is that it'* going to turn out to be a weak battery or its connections, and the bad noise she hears is a rat-tat-tat-tat noise of the starter not quite engaging. If she was hearing the squeal you get from a misaligned starter (similar to when you grind the starter into an already-running engine by mistake), I think she'd be a lot more scared about it.

I would do a thorough cleaning of the battery cables as we described, then drive it for a day or two before doing anything more expensive like buying a new battery. Give the existing battery a chance to benefit from your improved cable connections, like getting a better recharge from the alternator, before you throw any more money at it.