How long does it take for a horse's tail to grow?

I ended up having to cut my mare's tail pretty short last fall... now it's sitting a little above her hocks. Where i live, the weather is getting warmer, and the flies are starting to come out. Do you think she has a long enough tail to get her through fly season? How can I get her tail to grow longer, quicker? Any advice is much appreciated(: She used to have a tail that nearly touched the ground, and it was super thick.. i felt so terrible when I had to cut it:/ It's still thick, just not long.. and i miss it:/ Also how long do you think it will take for it to grow all the way back out?