There could be so many different different things causing your DD's wakefulness at night. Is she upset or does she seem in pain when she is awake at night? My DS was 8 weeks prem. He was & is a terrible sleeper bcus of reflux & ear pain.
The doctors did say that prems get used to the bright lights & noise in the NICU/SCN so maybe try having a soft background noise with a night light on. Have you checked the temperature of her room at night? It needs to be fairly cool (but not too cold) for them to sleep well. Is she hungry/feeding well before bed? Could she have reflux/colic waking her up? Was she wrapped when in hospital? Are you still wrapping her? Are you sticking with the same routine each night to help her know that it is bedtime? The list goes on....
However your routine works but if you do stick with the same pattern of events she will know that it is bedtime, for example; quiet playtime/tummytime/cuddles, bathtime, feed, nappy change & lay her down to bed so that she learns to settle herself to sleep instead of being cuddled off to sleep. Try to keep to the same time each night. Kids generally respond well to predictability.
Hope she settles down for you so that you can both get a decent sleep.