Hello and welcome puffin, - so sorry to hear about your mum, - she's had an awful lot happen to her in a very sort space of time, so she'll be feeling very shocked and a bit bewildered I imagine.
It sounds good that they think they have caught it early, I know its very hard waiting and not knowing, and she will probably feel a bit less panicky once she knows what her treatment plan is.
I would guess (although I'm obviously not an expert) that what type of cancer it is will determine whether they think she needs chemo, - with some of the faster growing types they may offer chemo just as a sort of 'mop up' job, to be extra safe, also the fact that it was in an awkward place will influence their decision. (IME they have interdisciplinary meetings between surgeons and oncologists where they discuss the best treatment plan for each individual, so they will be working out the very best plan for her).
Its tough - especially as she doesn't know what's happening yet. She'll be feeling sore from her surgery and it can take up to a couple of weeks to get the GA out of your system. Plus it's emotionally a hard time - very common and normal to feel a bit down, or weepy at times.
Does she have someone to go to appointments with her? - a bit of moral support is very helpful IME, also a second pair of ears - it's sometimes hard to take in everything they say when you're feeling a bit scared and overwhelmed (writing things down is a good plan too)
You sound like a lovely daughter, who will be a great support for her 
- its really often a case of getting through it all bit by bit, - deal with each bit of treatment as is comes along, and try not to get too ahead of yourself thinking of all the 'what if's'
loads of good wishes to your mum - and you too. You are very welcome here, hope we can help a bit (and of course your mum would be very welcome if she is a computery person )