Puff - I'm sorry to hear she does have a tumour, but it's very good that it is small and they have found it early - before she could even feel it. TBH I don't know whether they will offer mastectomy or another lumpectomy - it depends on various factors - position of the tumour for example and how close it is to the chest wall.
Once it is biopsied, they will have a clearer idea what the best way forward is, - if it is small and hasn't spread to the lymph nodes, then she probably won't need chemo, also they would take her age and general health into account before suggesting chemo. However if she does need it, it is doable - its not a walk in the park, but I think people generally anticipate the very worst, - most people get some, but not all of the possible side effects, and hospitals are very good at deal with S/E's. - But that is looking too far ahead
- she may very well not need it. I'd say she has a pretty good chance of avoiding it given tumour size.
She might be a candidate for herceptin, - it is given routinely now fro early BC, if the tumour is one that is responsive, - I should think when she had her first tumour herceptin was still only being given in advanced cases. Again herceptin is very doable, - a few s/e's but not usually so bad that you can't carry on with your normal life.
Do feel free to ask me any questions you like, or that your mum would like answered - I will do my best to answer (PM me if you'd rather) - I have had a mastectomy, a lymph node clearance, chemo, radiotherapy, herceptin and tamoxifen - so know a bit about those things, And as I mentioned before the ladies on the tamoxifen thread will be happy to chat to you, - don't worry about following what's going on on the thread - we tend to go off at a tangent, but dive straight in with your queries and someone will answer you 
very best wishes to your mum 