I don't know what the market is like where you're at. But where we are, if a tenant asked for those, I would say - no thanks - do you want out now or later? Having said that, it all boils down to numbers for your mother. Would she lease to a new tenant at those terms? If so, then it's probably a good deal for her as long as it doesn't cost her much to reconfigure the space.
However, if what her realtor said is true - that she could probably lease the whole space within "a few months," for the full current rent or higher, I would bail and look for a new tenant. I'm not averse to rent forgiveness or lease modifications but I always look at it from a net dollar point of view. If it costs me more to keep the current tenant I say no. I've had it come up a few times, and even twice with the same tenant. Amazingly enough the 2x tenant has become a long term no issues tenant for us.
It's also important to establish whether she can afford to carry that space empty for a while. In the end, if you say no to all their demands, they may still stay if the store is truly profitable. She should, however, be prepared to have them terminate and move out if she calls them on their move.