Help me understand diagnosis, please.

Grade 3 is an aggressive cancer which is why I would think her oncologist is wanting to do chemo first and that is to try to kill those cancer cells that move through the lymph glands or vascular system of your body.  It makes total sense to do chemo first when you are grade 3. 

There are other reasons to do chemo first with a large tumor and that is Adriamycin/Cytoxin followed by Taxol as in many cases this chemo cocktail can shrink the tumor to where the surgery doesn't have to be so invasive.  I had a 4 CM tumor that shrank down to nothing after doing chemo first so my surgery was a lumpectomy.

It is normal to have a bone scan and CT scan done along with an MRI.  The bone scan will show if the cancer has spread to the bones (a place that breast cancer loves to go to), the CT scan would show if the cancer has spread to any other organs of her body.  The MRI is done to see if there is anything else going on in her breasts that may not have been picked up on the mammogram or Ultrasound.  Do know that MRI's will show areas of concern that might not be a problem at all, so typically if the MRI shows other areas of concern it would be normal for them to schedule another ultrasound to look more closely at those areas.  My MRI showed areas of concern on my right breast (non-cancerous breast) but after having an ultrasound afterwards, cancer was ruled out of that breast and I only had it in my left breast.

There is a forum for chemotherapy and I would suggest that you go to that forum and look at the different threads that are pinned at the top.  There are some very informative threads on what to expect from chemo, how to prepare for chemo, and how to manage the SE's.

Between each phase of treatment is normally a 4-6 week period where no treatment is given.  In other words you do all your chemo, wait 6 weeks and do surgery, wait 6 weeks and do radiation.  This is to give your body time to heal in between the various treatments.  

Since her tumor is Grade 3, they wouldn't want to wait another 8 weeks or so to start chemo because the cancer is growing at an aggressive rate.  I am calculating 2 weeks to get surgery scheduled and then 6 weeks of recuperation prior to starting chemo.

I am not an expert like some of these women so be patient because someone will come in here and help you out on more of the particulars.

It is a scary time, not only for your mom but also for yourself but there are support groups, this on-line support group, etc. that can help you and your mom.