I think all of the above are great suggestions. I also think you could tell her to just be patient with herself and let the bond grow naturally, as her time with the babies continues. I didn't personally experience this myself, but it's not uncommon for it to take a little while before a preemie mama feels like her babies are really *hers* once they come home. Also, preemies tend to take longer to do the things that make you feel like the baby is a real person - smiling, laughing, etc. Once they reach that point and become more interactive, it's pretty hard to resist the bond.
She (and you, as a good friend) should also be on the lookout for PPD and anxiety, which could stand in the way of feeling closely bonded to her babies. Preemie mamas and multiple mamas seem to be more prone to both.
On the practical side, she can carry pictures of her little ones with her when she's away from home, and post little videos on youtube, so she can always look at them and remember what it's like to hold them. It might help her to carry a couple of their little hats with her, after they've worn them - I know that smelling and touching and just seeing their little hats that came off their tiny little heads always made me feel warm, somehow.
Good luck to her. I cannot imagine having to go back to work so soon after all that, but we do what we must. They will all get through it.