Don't worry, my dear. I'm sure your Rita will be very much your Rita, and she will be OC, so there'll be bits of JKR's Rita, too. And if other writers recognize a bit, they'll see it as a homage.
You wouldn't do anything that anyone could think of as theft, I'm sure.

I, for one, took kellychambliss's idea of Bridgeford as a Wizarding University (the most prestigious one, of course) and used it freely throughout my fics. And she's fine with that, because it is a homage.

Stop fretting and write, will you!