As long as there is poop and it’s not sticking to her butt so she’s always dirty there and need butt-baths, this is not extremely worrying since she’s always been like this. It’s when a bun’s poop starts to shrink and/or become much more sparse that an alarmbell should go off. Bunnies’ tummies have individual differences, just like people’s tummies. Some are sensitive, others are like feral goats.
As a rule though, more hay, hay that she likes (you can try different hays – all grass hays are fine for bunnies) is very good for a bunny that has a tendency to a slow gut. (Double poops and beads-on-a-string-poop signify a slow gut.) It’s great that she’s started to drink more, hydration is very important. Greens are also good, esp leafy greens, pellets should be given in moderation. Choose a pellet with the highest fiber content you can find. And you can try cutting some on the pellets and see if that encourages her to eat more hay. (Don’t cut out pellets, all dietary changes must be done very slowly.)