A.F.
Please don't panic! The symptoms you listed do not automatically point to Diabetes. My daughter was diagnosed at 19 months old with Type 1 diabetes and my son was diagnosed with Type 1 at age 6. My husband has had Type 1 since he was 3 years old and the strange thing is that this particular type isn't genetic!
Absolutely take her to the doctor, but decreased vision and numbness and tingling of the hands and feet are not common symptoms in a child. Please rest at ease until you can rule it out!
edit* Sorry, I wanted to add more info! :) My son and daughter both have perfect vision, so please don't worry about diabetes in that respect. Increase thirst in diabetics is hand in hand with increased urination and usually the urination is the major clue. I actually wouldn't get a glucose monitor without a diabetes diagnoses. It's absolutely not necessary if the blood and urinalysis check out.