If some might think it would be silly for a female character in a military setting to have long hair that isn't tied up, it should be worth noting that the Systems Alliance is fictional, and a sort of smorgasbord of various real life influences from the military to the navy etc. BioWare can do whatever they want with there new fictional military in Andromeda, if there is one, and this includes long hair.
It should be down to player choice with this. Some can have short and it be more realistic to them, others can have long and it not break immersion.
I'd be happy with or without. I say without, cause sadly BioWare hasn't been able to handle long hair. It's rare for there to be really good long hair in video games.

It's debatable I guess, but I liked the step forward in how long hair could be in video games with Elise from Assassin's Creed Unity.
Also long hair in an action/combat setting that isn't tied up? Not completely out of the realms of reality either, there are numerous examples in fiction of female action heroes who have long hair that isn't tied up and they are still competent.

Van Helsing was a fluffy film, but I liked Anna Valerious' character in the film.