I'm not DM, but I hope I'm a DM-in-training.
Basically, my weak 6 months of vet assistant training says that any change in behavior can be a "sign" of something, and excessive drinking seems to be one of the frequent warning signs of something wrong.
I could give you a few theories (could be anything from diabetes to thyroid issues to bladder infection), but the best thing you can do is get Daisy to the vet for a few blood tests - with one blood draw they can usually check glucose levels (diabetes), kidney and liver functions, and thyroid hormones (usually runs about $100-150 for the testing). Make sure to mention any differences you've noticed in her - the drinking, the peeing, eating normally? acting normally? lethargic? hyper? weight gain/loss?
Good luck with this - the good news is that by noticing it and checking ASAP you can hopefully catch things before they get too nasty.
Best of luck to Daisy! Keep us posted!