The other ladies gave really great advice, so I don't have too much to add.

I will say that last year, I signed up for a tri thinking I would be running a 5K easy by race day. Well due to a running injury and setbacks, come race day I had barely run 1 mile straight in training.

So, I just did a walk/run combo. I found a buddy and we walked/ran together. It was fine and worked out great. In fact, that I think that run time was the same as the other times I have RUN the entire distance in a race!

Good luck, you can do it!