Not a twin mom, but Amy was born at 34 weeks. I think 2-3 weeks is probably the minimum stay for 33 weekers.
She needs to pump religiously if she wants to breastfeed them exclusively. The NICU should have an LC and she should consult with her right away. She should aim to be pumping 8-10 times a day. Each NICU has its own protocol for how they want pumped breastmilk to be stored and labeled, so she needs to learn their protocol.
I liked the Sears Your Premature Baby Book. LLL has a nice little pamphlet called Breastfeeding Your Premature Baby. Both were helpful and gave me something to read during the downtime between feedings and pumpings.
Helpful things for your friend would be healthy, non-perishable snacks that she can take to the hospital. Encourage her to buy extra pump parts so that she doesn't have to wash so much in between pump sessions. (There are much stricter cleaning/sterilization guidelines when pumping for a preemie vs for a full term baby.)
Beth, mom to older DD (8/01) and younger DD (10/06) and always missing Leah (4/22 - 5/1/05)