I think if you can get back up to a 10K distance, you'll be ready for sure.
My Princess training was pretty bad--I hadn't run further than 5K since the beginning of November, and I just got through the 5K and the 10K with no problems, and I expect to survive the half marathon tomorrow morning with nothing worse than sore feet.
I would suggest you walk the 5K in April, and take it easy in the 10K, and save your energy for the 10 Miler. If you're not already using run/walk in your training, I highly recommend it.
I hope your ankle continues to improve and you have lots of fun with your first runDisney challenge.