^^^I think what she's saying is drinking only water instead of other things like soda, juice, etc. And making sure she gets her water in for the day by having a glass with meals, snacks at those times.
But yes...do your research. 25# of fat weight in 6 weeks is NOT a healthy amount to lose. That kinda averages out to 4# a week. The generally recognized number is 1-2# per week for permanent weight loss. You may find in the first few weeks you lose a big number but that is because you change your diet and cut down on salt, and (TMI, get ready for it) when you eat cr@p like chips, cakes, treats, sugar, non-nutritive food...your gut is PACKED with the stuff. Your digestive system is probably holding 15-20# of waste as we speak. So, when you start eating fresh things like veggies and fruit and "real food" your intestines will clear and you will be lighter from that. Which is good, but just don't be illusioned thinking you've lost 15# of fat in the first week. ;)