WOW! Mine were anything but a surprise. I can't imagine not having time to get used to the idea.
The fact that you're going out to help her is probably the best thing you can do. It's at a good time, too, when the help usually starts to dry up. I needed as much help as I could get for the whole first year, and particularly the first 9 months or so.
When you get there, cook her dinner, play with her older kids (who will probably be going through a tough time because mom will be so busy with the babies), and clean for her. You're probably already planning to do that. For me, I actually appreciated having people hold the babies because I felt like it was hard to hold them enough.
If there's a grocer who delivers in town, give her a gc for them. Help her find a teen who can help around the house for a few dollars an hour. With twins you basically need a clone, so the more hands the better.
For BFing, ask her if it's hard, but don't imply it's impossible. Listen when she tells you that she never gets up off the couch and that she is literally feeding constantly. Help her get really good help from someone knowledgeable about TWINS if she has trouble. Buy her the LLL book "Mothering Multiples." Sub her to the APMultiples list on Yahoogroups, which is run by the author of MM.
Get her a doubleblessings foam twin nursing pillow. Get her two slings. Be gentle with your AP expectations for her and help her be gentle with herself. You can't do everything the way you want to and that is hard. MOTs often need to let go of a lot of guilt.
Definitely call, but understand if she can't talk or doesn't call you back. Catch as catch can and know that her weeks are slipping by in the blink of an eye. Let her know you understand and you'll be there when she resurfaces. It may not be for many months.
Send her older kids cards and gifts to remind them that they're special and not just "the siblings of the twins." Twins get tons of attention and that can make the adjustment even harder for older kids.
Those are the ideas I've got right now. Hugs and I hope this helps. Congrats, new auntie to twins!