You may want to take this one in your granny gear at a moderate pace. Not being snarky just trying to help in keeping the sweat factor to a minimum. Like most everyone says shower, deo, etc. before leaving will lower your arrival prep time to a minimum. My rule of thumb has always been to not commute in my work clothes and not work in my commuting clothes. Allowing an extra 10 minutes for a cool down period is prudent.

http://www.nashbar.com/bikes/Product...7_10000_200350 looks like it may be what you may need from what you say about your work environment requirements. Keep in mind it's NOT waterproof, but can be made so by Thompson's Watersealer (inside AND out)and some well placed clear caulking along the seams. The bag has compartments for shoes, ect. as well. Of course you'll need a rack to go with it. Panniers will force you to roll your clothes to keep them wrinkle free and are generally more expensive.

The main thing, truthfully is to do a complete change of clothes upon arrival...you'll get the routine down. It usually takes me a week or so at a new job to figure out the timimg and storage limitation(s). Whenever possible I try to store my bike inside. And most co-workers respect and accept a cyclist's quirks and needs in terms of privacy. In over 20 years of commuting in 3 different states I've never had a problem w/anyone complaining or being impatient.

Btw, be sure to keep an extra supply of clothes and personal items at work as well as hangers for your commuting clothes in the event of getting caught in a rain shower. Unless you plan on full time commuting then you'll need them for your rain gear, too.

And there's a website http://www.teamestrogen.com that has a whole sub-forum dedicated to all things commuter female...you may want to check that out as well. Have fun! Cycle-commuting is a great addiction.