Hi Maria.
It sounds like your mum could be going through the menopause, although she just may be stressed as you said she is back in school.
I was diagnosed with premature menopause a few months back (im 17) and I noticed that i was getting hot sweats all the time, even when it was freezing cold. Also, I have terriblbe mood swings where I will be happy one minute and literally 2minutes later I will be screaming my head off over nothing.
In terms of making it comfortable for your mum, she may not want to talk about it as she may be upset about not being able to have children anymore. Just let her know your there if she does want to talk, and try not to take her mood swings personally.
Hope this helps.