I'd love to see her mane growing out of control because of some magic mishap

it would probably make for an interesting scene, or plot device.

Twilight wakes up to find her mane has grown abnormally long over night.

then learns the same is happening to everyone in ponyville.

maybe it was discord, and pinkie playing a prank

maybe rarity got a magic artifact so she could use her own hair to make new fabric

maybe it's pollen from the everfree forest

maybe the solution results in twilight having hair like celestia and luna

so many possibilities