Yes ma'am, you should do it. Gotta start somewhere. And seeing how much faster your swim becomes NEXT time, or next year, or whatever, will be very gratifying! Everyone--okay, not everyone, but most people, have a strong and a weak area in triathlon, and for plenty of people it's the swim. So knowing you're strong on bike and run, live with being not so strong yet on the swim and do it anyway. You'll have a ton of fun and want to do it again and your swim will improve.
"My predominant feeling is one of gratitude. I have loved and been loved;I have been given much and I have given something in return...Above all, I have been a sentient being, a thinking animal, on this beautiful planet, and that in itself has been an enormous privilege and an adventure." O. Sacks