Of course she has a choice and can decide to either hold out for a better offer or keep as a holiday home and as you say much depends on personal circumstances. If you bought purely for investment and hoped to rent out and have to, to cover a mortgage then taking such a low offer might be your best bet, but if you bought for personal use and do not need to free up the cash, then probably better keeping for the next few years and seeing what happens.
Clearly AAM would not pay market value for these properties as they want to buy stuff that is well below market value so they have the best chance of making a profit in a few years time. Don't think quality has anything to do with it. They do not appear to go and inspect any apartments, just send them an enquiry with details and you get back an offer. I am sure they know the main developments but they do not inspect individual apartments as far as I know.
Nearly everyone on here is very negative about Bulgaria, for good reason in many instances. There has been a culture of rip off the foriegners buying there, overpriced apartments, too much development etc...
However, it is not all bad. Bulgaria is a beautiful country, away from Sunny Beach and such places, has great weather, is much cheaper living than the UK and I know many people that live and holiday there and love it. Unfortunately most people bought off plan in the large, over developed and over priced resorts, never visited the rest of the country, if they visited at all and do not know what else is on offer.