I have three 3-month early preemies (well, they were born at 28.5 weeks, perhaps not quite 3 mos -- and they are now 14 year old).
The NICU (Neonatal Intensive Care Unit, for the uninitiated) is not a typical hospital ward -- talking with the nurses would be the thing to do -- perhaps they'll have some ideas of when the best time is -- and might provide some help. Our boys were in the NICU for 8 weeks
But I would not hurry things. No one expects a new parent to provide platinum prints of a newborn so soon! Take it slow and perhaps it might be better to wait until she gets even stronger and can be held outside the incubator for extended periods of time. A image of mom holding her, taken with the Rollei, might be the way to go...no need for the close-up work then. Those negs make for nice little platinum prints. Crank off 12 shots, and gang-print all twelve on a single sheet of coated pt paper and cut them up for the cards.
A digital image or two for now would be more than enough for friends and family. I have a great photo of one of my boys wearing my wedding ring as a bracelet!
I wish your daughter the best. But take care of yourself, also! The NICU can be a scary situation -- it certainly had it tough moments for me, even with everything going well!
PS...while triplets were a little bit more of a handful than a single babe, take advantage of this time. While the boys were in the NICU, I got a lot of darkroom work done. Once they got out (I was a stay-at-home-dad) all I time for was SX-70's! HINT -- and take advantage of the time before she learns to crawl! Until then, one can have a lot of fun with photos as one can place the babes anywhere and photograph without having them crawl off!