K.,
I'm the mom of 3.5 year old boy/girl twins and some things that were great:
Graco Snugride Infant Seats with matching double stroller. They come with bases for the car and like someone else said, they snap right into the stroller. I really, really missed them when my kids outgrew them.
If she's having trouble sleeping, the Total Body Comfort Pillow from One Step Ahead. I also used it for afterwards for those in the middle of the night breastfeedings. I could keep a baby up higher up between my husband and myself so if I fell back asleep, I wouldn't have the risk of them getting trapped under the covers.
Fisher Price's Ocean Wonders Swing. It was a fun place to let one sit while I was tending to the other. She only needs one.
Tiny Love's Gymini. My kids loved this!
The Baby Einstein bowls with the rubber ring bottom. Don't bother with the spoons.
Baby Einstein videos and books. The Baby Babble DVD is also great; it's by a couple of speech pathologists and also has tips for parents to encourage speech.
Knit crib sheets, not cotton. The knit ones fit better, no matter which mattress we used. Also waterproof mattress pads.
Convertible crib(s). My mom bought us one even though we knew we weren't going to use it for a toddler bed. They shared a crib for while, and then we bought a cheaper one. The convertible crib only needed tightening of the bolts twice in over three years; the other one needed constant adjustment.
Prefolded cloth diapers for burp rags. Don't bother getting the cutesy burp rags, they don't do nearly enough.
Cabinet Flex-Locks by Safety 1st. Only lock that my two still haven't figured out. We're still using one on our side-by-side refrigerator!
Furniture straps. Two children working together can pull bigger stuff down far easier than one child working alone.
It's difficult to buy clothes for twins early on; moms get too many onesies and cute outfits in smaller sizes that the kids never wear, but until you get an idea of the growth rate(s), it's hard to buy ahead on sizes (re: seasons). If you do get clothes, get stuff with snaps at the bottom for easy diaper changes.
Stretchie foot pajamas from Children's Place. Once they start moving, they were comfortable and not baggy so as to restrict movement. Look for a sale - usually 3 for $25.
A copy of Chicka Chicka Boom Boom - my kids still love this book.
The old-fashioned wooden alphabet blocks.
Wipes, diapers, Diaper Dekor Plus Diaper Pail and refills.
If your friend is planning on making baby food when they're ready, the book "Super Baby Food" by Ruth Yaron and a good blender that grinds.
I know I appreciated someone helping me with the housework stuff occasionally so I could concentrate on my kids. Most people want to visit with the babies not realizing that one of the biggest stressors for a mom of multiples is falling behind on everything else and not getting nearly enough time to just sit and play with your babies - you're dividing your attention between two needy individuals instead of focusing solely on one.
If you can commit to the time and are willing, "coupons" for other housework like shoveling the walks, putting up shelves, trimming the hedges, mowing the lawn, help with spring cleaning, etc. If someone's by themselves with the babies all day, it's very hard to get these types of things done. I didn't get to wash/clean my curtains for almost 3 years! LOL! Never did get this gift, but I could've used it. :-)
I never used the Pack 'n Play; don't bother. Most toys until they get much older you only need one.
A subscription to Twins Magazine.
If she has a digital camera, maybe some prepaid prints from Snapfish.
Hopefully she won't need this, but my son was in NICU for a week and we were "nesting" at the hospital. Some friends brought us food and drinks; microwavable soups, cereal bars, etc. after I complained that it was costing us more in cafeteria food than the copays for the doc visits to have the babies! It was the most thoughtful and useful thing anyone could have done for us at that time.
Most of all, a willing ear and shoulder to remind her that she's not going insane and she can handle it all. :-)