Hi Kimmy
I have these trembling attacks when my blood glucose levels drop below 4.7 and they have always happened when I have used too much energy, or gone too long without food. A quick snack - sandwich or biscuit - usually stops it. I'm told that sugary drinks and sweets aren't as much help as something starchy, but if that's all you have, it's better than nothing The thing is, to do something to stop it sinking lower, when you will reach real hypo levels. You could just regard it as an early warning really, so although it feels really odd, it's not a bad thing for it to happen at a slightly higher level than normal.
I guess everyone's different in how they feel when sugar levels drop but your mum should monitor her levels if possible and maybe check her medication with her doctor or nurse to make sure her control is as it should be.
Hope your mum is feeling fine now.