Mom won't talk to me about her Diagnosis- for the 2nd time

My mother who is probably the youngest most active and healthy 53 yr old nurse around was just diagnosed with breast cancer again.  She was diagnosed 5 years ago and they performed a Masectomy on her right breast.  After reconstructive surgery she was able to create a new breast from fat in other parts.  Now 5 years later we found out from her 6 month check up that she has a mass in her sentinal lyphmatic node in the same breast.  After a biopsy found that it was cancer, she is having a PET (full body) Scan today and awaiting results.  She is lucky to be very good friends with the Head of Oncology for a large hospital in Philadelphia- so she is in a good spot care-wise.  She just won't talk to me abotu it all.  I'm convinved the only reason I know about all of this was because I was with her, shopping at the beach when she got the call from her doctor.

I really don't know much abotu the situation- and she won't give me or my family many specifics in fear we'd worry too much- her first thought after getting off the phone, who will take care of the dog and my dad, and for me to NOT tell my sister, and that we'd wait to tell my dad. 

We all live about 3 hours apart I just happened to be in town (to be there when we got the results good or bad) and my dad, who lives with her is battling his own rare disease in his eye- so she tries to buffer information so he doesn't worry too much.

I feel so lost and I feel like i can't ask her about anything because when I do, I can just hear her voice start to shake and I don't want to make her cry.  I know everyone deals with things differently but after the first time around I just felt like we did everything right- were so precautious, so thankful, it was like a second chance, she was already a really healthy person, eating right, working out, and taking every preventative vitamin, or medication under the sun and I definitely showed my appreciation more...since the first time around i didn't know it was as bad as it was...  but now I feel so lost- I'm right here, matured, and ready to be the shoulder she needs and I want to know everything but she tells me and my father to not go to Apts with her, she takes her sister, since she is a nurse.

I feel really left out- I want to help- All I can do is pray.  Has any other young women been put in the same situation?

Are there certain things I can say besides the obvious that I'm there for her?

I don't want to upset her but I want to be more knowledgeable about everything that's happening. I can't even do the research or anything because I hardly know anything about her condition. 

 Is it regular to breast cancer to occur after a masectomy?

 if it's in the lymph nodes does that mean it will travel quickly in her blood?

What is radiation/chemo? How often does it happen?  1/week 1/month?

Any answers, support and even prayers are Greatly appreciated...