Respectfully, I think you're conflating 2 different issues.
When a vendor misrepresents something or changes the terms after representing what they are, that's essentially "bait and switch". You've seen yourself how damages may be incurred as a result - for example, while I'd never do such a thing, there are several people on this forum who have sold their family vehicles in preparation for the delivery of their new Land Cruiser. One guy even admitted to forking over the cash before his vehicle had even hit the dealership.
If a dealer refrains from committing to a price in advance, that's one thing, but to accept your deposit based on an understanding that you'll be paying MSRP, only to change their mind later because they (allegedly) had a better offer is not an ethical way to conduct business. She should be entitled to that vehicle at MSRP, if that indeed was the initial agreement.