Martaw, Zen & I are both about 5'1 (least I am and she's not much taller).

What's your inseam measurement? This is where fit starts coming into play - women's specific design (WSD) bicycles are made for women who have relatively long legs in proportion to their body, and short torsos. So if you have a long inseam, then you might want a WSD.

What part of the greater DC area are you in?

I mostly get my bike stuff online... I've gotten reasonably handy about doing most repairs or installations myself, and what I can't manage, my bf can... I've currently got 4 bikes - 2 road, 1 flat bar/road/commuting/rough road bike, and 1 mountain bike. 2 were craigslist purchases, 1 was an ebay purchase, and 1 was a frame someone was selling on here that I built up... So I definitely believe in buying used... However, if it's in your price range, most people recommend going to get a good bike shop and having a professional fit done & having them set you up on a bike for you.

I'd just say that while you're still getting used to cycling again, buying a bike somewhat like Zen's is a good idea - it'll be something not too intimidating and comfortable to learn on, get your cycling skills back, and will let you explore cycling to figure out what you really want in a bike... and then go get that. And then you'd still have the first bike to use as a commuter or towpath or trail bike as well.

I wouldn't recommend you buy a bike online, you really need to test ride now.

So sites to look at for buying stuff online:
teamestrogen.com
reioutlet.com
backcountryoutlet.com
performancebike.com
nashbar.com
sierratradingpost.com
bonktown.com
chainlove.com
realcyclist.com

If you're interested in a bike or other cycling related items - you can always post on here to see if someone's tried it or what people think.