If the baby is 5 weeks early, she's likely looking at 1-2 weeks' NICU stay at the very least -- which can be pretty overwhelming even if you've done it before!
Ways you can offer support might be:
- offer to babysit her older child so she can spend time with the baby/take a shower/sleep/ whatever
- buy a preemie sized outfit or two that she can put on the baby right away (all the babies in the NICU are always dressed all alike, in hospital gowns and such -- if it were me, I'd want my baby to be wearing her/his own clothes, at least, if it's feasible.)
- buy her gift certificates for the hospital cafeteria or coffee shop (especially easy if there's a Starbucks there or something -- lots of hospitals do) so she can grab food while she's at the hospital with the baby
- organize a few of her friends to drop off a series of meals for her - check to see what kind of frequency would be best for her before you set anything up. I know that for us, each meal brought over by a friend lasted us 2-3 days, so maybe a twice-a-week dropoff for a few weeks would be all she'd need. There's a pretty good format for organizing this at http://signup.pleasebringit.com/faq/ -- all you do is set up a sign-up sheet online, and people can select what they want to bring and when.
- We really appreciated having a few frozen meals from friends that we could just pop in the oven or microwave when we were stuck for a meal. That might be a nice idea to provide support for your friend, too, once the baby comes home.