Welcome to TE . . . (from a native Pittsburgher, now living in exile)

I'm 5'1" and I ride a Rodriguez Rainier size S1, which is effectively 43 cm.

Some companies have long-distance test-ride programs, which you may want to take advantage of since it can be challenging to find an LBS that stocks small bikes. Or if they do stock them, they sell rather quickly. I know that Rodriguez has a program and Terry has one, too.

You should also look at the bikes for sale thread on the Terry website.

Also check out Surly Cross Check and Long Haul Trucker.

If you think you'll be out in poor weather, you'll want something that can take fenders, even if you don't put them on initially. And if you're out in the winter, I imagine there will be other issues with keeping your bike clean after riding on a slushy, salted street. I imagine you can run a search for advice in those conditions . . . last time I was on a bike in Pgh I was probably 11, riding my Schwinn Fair Lady, and it was a summertime thing . . .

Good luck!