She would look lovely with a pulled mane - but the decision is yours.
To pull such a long mane you wouold want to spend several weeks doing it as she would be uncomfortably sore if you do it all in one go.
The aim of a pulled mane it to get the mane the same length and thickness from top to wither. So you work on a mix of scissors and a pulling comb. I use a dog comb with a handle on it as I find it is less likely to break the mane off. Thinning scissors and hair scissors.
Start by looking at the hair by the withers, noting the thickness of the mane here, often I just shorten this with scissors. Take a few long hairs, and with the comb back comb the rest of the hairs out of the way. Cut the remaining hair at an angle to the length that you want the mane to finish. Keep doing this until all the hairs are the right length.
Now work on the rest of the mane - best done when the horse comes back from work and the pores are open - hair comes out more easily. Grasp a few of the longest hairs and back comb the rest out of the way, wrap these hairs around the comb and pul quickly to remove the hairs. Rub the horses neck quickly to ease the discomfort. Some horses hate having their manes pulled but generally get used to it and tolerate it if you don't do to much in one session.
Work your way along the mane randomly removing long hairs. Repeat this every few days until either the mane is the length you want or the thickness you want.
If the mane reaches the thickness you want before being short enough - you will need to finish it as you did the area near the mane. If it is short enough but still thick then you will need to use the thinning scissors.
Work mostly from the underside of the mane with the thinning scissors back combing some hair out of the way and cutting across at an angle with the thinning scissors.
To help reduce the discomfort you can try rubbing oil of cloves into the skin, this numbs the skin slightly and makes it less painful.
Take your time pulling the mane - a little every day is best and then keep it tidy by pulling a few hairs every few days.
A picture after would be nice. I like my manes about 3 - 4" in length - I do small English plaits for shows and I like them small and neat.