Yay Pandita. Trying new things is scary, but so fun and rewarding too. Irongirl would be a terrific first race. I haven't raced that brand, but I've done Danskin and another women's only race a couple of times. The women's only races are a great way to get into the sport because they typically offer a very supportive enviromnment and the ratio of first-timers will be significantly higher than at other coed events.
My 2 cents:
1. As others posted below, beginnertriathlete is really good. They have good beginner training plans with swim workouts, etc.
2. Rachel is right on the money. A little bit of open water experience goes a long way. One of my favorite bloggers DC Rainmaker,
https://www.dcrainmaker.com/p/washington-dc-resources.html is in DC and has a whole section of his blog dedicated to tri resources around DC, especially as it relates to open water swimming. Just remember, never go alone.
3. Do you have any friends you might be able to convince, blackmail, or otherwise to do it with you? Having a support system and someone to work out with can give a huge boost.
4. Many races offer resources to participants, for example, they may run an open water swim clinic or transition clinic. Be sure to use whatever you need. My first tri, Tri for the Cure offered a free training plan right on the website that I used.
Is Columbia, MD near DC? If so, I found this:
https://www.tricolumbia.org/IronGirl/
Getting into tris has definately changed my life for the better!!!