I have to agree with mamadoc (I am also a doctor)- it may well have been appropriate to make your mother nil by mouth (even though she is a diabetic) if they were concerned about an unsafe swallow (with consequent risk of aspiration). Regarding your concern that she should have been intubated, I can assure you she should not have been intubated unless she was needing assistance with breathing (i.e. ventilation). If she was made nil by mouth, she should have had a drip for maintenance fluids. As a Dr, I would be wary of making an assessment- unless it was a stroke physician, as our training in this is minimal. If in doubt, I would have made her NBM and awaited formal SALT assessment. Our hospital has an on-call SALT at weekends/Public holidays (not overnight), although I know not every hospital has this resource.
Is your DM an insulin dependent diabetic? If so, in these situations they should have used a "sliding scale" which is a way of controlling blood sugars using IV insulin and dextrose fluids. If she isn't a insulin dependent they should have been keeping a close eye on her blood sugars, but would not start a sliding scale, as she is at much lower risk of complications from being NBM.
You should have been made aware of the decision to make her NBM and why. However, from experience I can tell you that this can be tricky to do in a timely fashion- family tend to come in the evenings, or afternoons at the weekends, when it is the on-call team who are there. They will not have made the decisions that day regarding your relative- and more likely than not, will not even be based on your ward. They will be able to read the notes to find out the plan made by the day team/recent results etc, but will probably not have an intimate knowledge of your relative's condition- or know what decisions have or haven't been discussed with relatives, until asked to speak with you by our nursing colleagues. Even when this happens, if we have unwell patients to assess, then speaking with relatives will have a low priority- and they may have to wait some time.
To explain this- at my hospital (fairly large, teaching hospital), in the evening (between 5 and 9) and at weekends there is 1 junior doctor for every 3 medical/surgical wards (excluding medical/surgical admissions), 1 for the orthopaedic wards. There are 2 senior medical and surgical registrars for the wards and 1 ortho registrar (also on-call anaestetic reg, and various doctors for other specialties such as paeds/obs and gynae). The on-call teams will do 13 hour shifts. So the junior doctor/registrar will be on their "home" ward 8am-5pm and then cover that ward and another 2 wards in the evenings. At the weekends, they will cover all 3 wards 8am-9pm.
So you see, while I completely understand that you would have wanted to be told immediately about this decision and why it was deemed necessary, I can see from the other side why it didn't happen. It's not because staff can't be bothered, it's that we only have 2 hands and can only be in 1 place at a time. That doesn't excuse the lack of fluids given, nor does it mean poor care is acceptable. I'm not convinced that the original decision was poor clinical decision-making, the problem is not making appropriate measures were taken subsequently and poor communication with you.
If I were you, I would complain about her not having a drip if made nil by mouth (and any other concerns). The fact that staff are encouraging you to complain makes me think they are also fed up with the way things are.