Could just be a growth spurt so she's hungrier.
When my son would get sick, we would always get "off track" & slide back. It would take about a month to get back to where we were.
My son was different and didn't sleep through the night until he was much older. He was a very active baby & was honestly hungry. Also, my breastmilk dried up very early so he had to have formula. That may not have filled him up as well. So he woke up in the night maybe more often than a lot of other babies (esp girls, I've found w/my friends that have girls). I just stuck with what he needed & it worked. We finally got through that stage and one day it all came together. He would sleep a 5-hr stretch sometimes but it took awhile longer than your daughter's current age to get him to sleep through the night. Hang in there & do what YOU feel your baby needs.
I say go in & try to nurse when she wakes up. Hopfeully it will just be a phase & she will most likely get right back on track!
Hang in there. I know it's tough but you'll get through this.
Btw, my son was 1 mo premature too so he was behind in development until abut 1 1/2 or 2 yrs of age. Now he's in the 95 percentile.