Both my mother and my partner's mother have both had it.
My mum had it about 20 years ago, and I can't remember much first-hand other than that my dad had to cook for us (We nearly died of starvation) whilst my mother was in hospital getting radiotherapy. She's fine now, though does occasionally get crippling and sudden pains that she attributes to the radiotherapy damaging nerves but as she says herself it's a small price to pay to be alive.
My partner's mother had it nearly 8 years ago now, they didn't really catch it early and had to have one breast removed but has not had it come back since.
So fingers crossed, your mum will be fine especially if as you say it's been caught early. Stay positive and don't worry too much.