Sorry to hear about your friend, You sound like you will be a very good friend. :)
I'm just coming to the end of my BCN treatment, doing rads ATM (done matectomy + node clearance and chemo) Things that helped me :
Little things to help with kids, collecting from /taking to school if I had appointments or feeling rough on chemo, taking pics at sports day when I was too ill to go, taking kids out for the day on my worst post-chemo day in the school hols, doing extra "mums taxi" trips for after school activities (we normally share). All of this offered rather that me asking for help ( which I am very bad at!)
I had one friend who went with me to almost all my chemos, that really helped.
Also just being a listening ear when she wants to talk about it, but don't go on and on, take your lead from her, sometimes it's good to talk about other stuff and forget what's going on for a while.
The old saying is true that you find out who your friends are in times of need. Most of mine have been brilliant, but one I had thought a good friend (and I hope I'd been a great support to her the year before when she found out her H was having an affair, followed by a very messy divorce) has texted me three times in 7 months (I didn't even reply to her last text...) So just be there and keep in close contact.
As far as prognosis goes, you can't really say how any individual will do, but the treatments for BC are amazing now and for lots and lots of folks they can get secondaries into a "holding state" for many, many years with the new drugs they have. I hope and pray she is one fthose people, it seems especially hard and unfair to be dealing with this when you have young children.
If you have any specific qus do pop on the tamoxigang thread, lovely bunch of ladies on there and chances are someone has been there before. :)