Not just one braid...

[Eskara1862]

Adorable! I had one Braided Beauty that I braided each of the four colors in her mane and then put the four into one large braid. It looked pretty cool. Unfortunately, I don't have pictures of it =(

[zombienixon]

I never did anything fancy like that, but I have braided my ponies' hair before. The only one that has braids is my Build a Bear AJ, to go with her Gala outfit.

[Chrissytree]

All my brush and grow ponies were treated to special hair do's. There was even a competition in the UK Club for pony hairstyles and I think I did something very similar to yours as one of my styles Three small plaits made into one larger one.
My speciality was a french braid from the front of the mane adding little sections at a time to the bottom. Curly Locks has that done on both sides