I prefer my women to actually look like women.
The only time short hair is acceptable when it's tied up.
Long is Hot short Sexy
On her? Long. She's too tall to carry of short hair without it making her head look tiny on a lanky body.
Crab - long
Monkey - short
Cat - short
Bee - long
Phoenix - short
Vamp - long
Usually those that can pull off short, can pull off long even better than those who would normally look good with long
Short is extremely feminine though
Women are meant to have long hair. Pic related.
Truly cute girls are just as good with either style, but usually long hair is better (except braids).
Black and brown > blonde, with not red > red on the side, IIRC. Brown and black should be similarly common, with some red-brown and top-tier red-black mixed in, blonde (and especially blonde-red, aka redheads) being nearly absent in non-white populations.
Head pat fragment
That's zokuowari cover.
She still has twintails in later novels though, as you can see in her shot in the last episode of koyomimonogatari, and in said cover if you look carefully