the OED list numerous uses for: dandy, n.1, adj., and adv.
technical and other senses - preceding to things considered neat,
colloq - anything superlatively fine,
bantam fowl, and a jug of whiskey
and lists an example of a dandy woman:
1897 S. Hale Lett. (1919) 319 Mrs. B. was a dandy, she didn't fuss
entymonline says of dandy:
dandy is diminutive of Andrew (as it was in Middle English generally). OED notes that the word was in vogue in London c.
1813-1819. His female counterpart was a dandizette ...
The frequency of use is moderate overall. In these times I believe you could use 'dandy' for all manner of things, including genders. Certainly other are. See this recent article An Ode to That Rare Creature, the Female Dandy originating from N.E. America ... where all 'proper' thought arises ... at least in their opinion!
And this from of all places ... Britian: Why Female Black Dandies are the Ultimate Rebels
In fact I myself own a right dandy dog ... bred in England!