I think the most important thing is to listen to the consultant, make sure you understand what he/she says & repeat it back to make sure.
Your mum is not in for an easy ride, surgery will knock her back for a bit, but (from my experience) the pain control was excellent. Major things from the op are fatigue and discomfort from having so many tubes, etc attached and being stuck in bed for days on end.
I'm assuming she'll have a temporary trachiostemy (ie a breathing via a tube inserted into her throat) in which case make sure she has lots of biros & several pads of paper (both go walkabout in hospital) as she won't be able to talk until it is removed (typically 3 days or so). You may like to ask about this.
You should ask how long the op will take, the extent of the surgery (will depend on how advanced the cancer is), when you'll be able to see her & how long she's likely to be in hospital for. You also need to know what you should bring in to hospital to make her stay as comfortable as possible. For instance she won't be able to wash normally at first, so face cleansing wipes may be a good idea. TV arrangements vary between hospitals. Books, magazines & a portable radio with earphones could all help. Depends what she likes, but variety helps to fight the boredom.
I do believe a major help to recovery is to treat the whole thing as a game/battle to be won and to celebrate every small milestone (each tube removed, getting out of bed, being allowed to go to the day room or hospital shop, etc.)
Hope this helps - anything else, please ak.