That is fantastic. My DTDs were in intensive care for 4 & 5wks so he is doing super (and boys tend to be a little weaker in general).
I never even tried expressing through the night. I was not told to express through the night. Even though I didn't express overnight I managed to exclusively provide EBM for 3m. (well apart from teh time they had to have formula cos teh nurses forgot to defrost my EBM).
If she has a hand pump as well as hospital pump she could double express sometimes. I did this when I was at home (so mornings and evenings) and I think the double pumping really boosted my supply.
A bath will probably help too - relaxation. SHe has probably has milk but by evening she is so tired and stressed that she is struggling to get letdown more than not having milk in the breasts. Then she gets more stressed about it, and so gets into a vicious circle.