It does *not* matter that she is not showing the "major symptoms" of Cushings - that's why it's SO grossly under-diagnosed and misdiagnosed! My dog Wylie is 12 and was diagnosed w Cushings around 4 yrs old...after being misdiagnosed for a YEAR.
Hair loss is a HUGE sign of potential Cushings. With Cushings, there is no rule that says a dog must have "X" number of symptoms - no no no.
The very, very first test you do any time you just suspect Cushings is the Cortisol-Creatinine Ratio Urine Test -- it's *not* a diagnostic test - it's a test that will tell you whether or not you should indeed further pursue the actual Cushings tests.
Here is an overview about Cushings:
Cushings (Hyperadrenocorticism) | | Long Beach Animal Hospital