Hi S
Yes, there are Hypo alarm wrist watches that can be bought, I tried one a year or so ago. I found it useless to be honest. There may be better ones on the market but mine had a mind of it's own and went off when I wasn't Hypo, and didn't when i was. Also the sensors do make your wrist sore. There may be other makes out there which are better, but I gave it up as a bad job.
I think it will be worth your Mum getting in touch with her Diabetic team and asking them to fit a Continuos Glucose Monitor, this is attached to your Mum 24/7 and will see the patterns of Blood Sugar throughout the day and night . Just a week on one can make all the difference.
Also, I have been Diabetic, Type 1 for 20 years, and I never had night time Hypo's ,then all of a sudden Whamo, they just started out of the blue. I had been on Lantus for years ,never a great Insulin for me in retrospect, but I did manage . The thing that stopped my crashing night time Hypo's, and day ones, was changing to Levemir, it stopped them in their tracks. Sometimes certain insulins change or we do, and what once worked for us does not anymore. I have never looked back from the change.
Just a couple of ideas, first of all a visit to her DSN should be her first step. Also she should set her alarm at 2/3 am then again at 5 am and just see what is happening for the next few nights, obviously she will need to have some fast acting Glucose by her bed. I found with Lantus it would drop me so fast than sometimes I was incapable of moving to treat myself. The Levemir does not do this.
I hope your Mum get sorted out, night time Hypo's are a real constant worry for us all. Shifts in other Hormones can cause Hypo's also as you said stress does do it for some people, though stress for me sometimes works the other way for me and raises BG. It really is all about testing regularly and seeing patterns.
Hope she gets sorted.