Do you think this has been happening for a long time, or is it new?
The assessment itself is OK - looking at your face and throat, then you need to try a few different foods and drinks. It can even be just someone sitting and watching while your GM has a meal.
If the speech and language therapist thinks that your GM's swallow is unsafe, they might recommend that she is placed nil by mouth. The doctors should then think about the cause of that - is it a temporary thing, like a chest infection or a urine infection, or something more long-term? Your GM also of course should say whether she wants to try being nil by mouth or not. Do you think she would be able to make that kind of decision? If not, what do you think her wishes would be?
If it's an infection, then it's really sensible not to eat for a little - you've heard the phrase 'starve a fever'. The doctors would think about feeding/drinking another way - so, probably IV fluids and perhaps a nasogastric tube. The SaLT should then review in a few days and hopefully things would have settled down and your GM could have things by mouth again. If not, the doctors have to think what options they could suggest.
It might be that, whatever the cause, your GM can eat and drink safely, but the SaLT might suggest changes to her diet, or to her drinks. She might suggest thickening drinks - this can look unpleasant but sometimes it's not so bad - particularly if it means your GM won't be coughing on every mouthful. Thickening slows fluids down so if your GM's swallow is weak and slow, she has time to drink without it going into her lungs.
I hope all goes well. The SaLT service in most hospitals can take 2 days to assess (usually Monday to Friday) I'm afraid. Don't ever be afraid to keep chasing for assessment or review, or to ask for more information if you aren't sure what's happening.