Does aviation MOSs have relaxed grooming standards?

No. Aviation crewmen have additional safety requirements in place specifically designed to preserve their ability to continue their performance of their duty. In this case, styling the hair to conform to normal requirements would degrade the helmet's ability to minimize the potential for her cranium being reduced to a mush that would preclude her from performing her duties. Her readiness to act as an aircrewman is obvious by her helmet at her feet. The fact that non-aviation personnel are unfamiliar with air crew specific requirements has caused conflict since DOD bought their first aircraft. Of course we could eliminate the discussion by requiring all personnel to report for duty in their dress uniform, then change into their utilities or combat uniforms when they are actively involved in infantry training, but that would be an incredible waste of time.

Never Wrong SGT Cody Voye!
As a female, with long hair, I definitely complied with the Army Regulation which clearly states a female’s hair cannot touch the collar. I was actually corrected by a civilian once while in AIT. I would certainly hope You would make this correction...just my two cents.

Yes. Women west the hair down when flying, otherwise the flight helmet will not fit correctly.

https://www.google.com/amp/s/http://www.military.com/daily-news/2020/08/27/air-force-considers-allowing-ponytails-other-hairstyles-women.html/amp

Maybe it is time to look at changing the standards.

I'd say that you were correct in approaching the senior member of the group, rather than the female corporal herself, and inquiring about her being out of uniform. I've yet to hear anything as outlandish as the response that you received. I've got one for the warrant officer though, BS!

Having spent 13+ years in Army Aviation with 8 of those as an Aviation Life Support Equipment/Systems Technician & NCO, I can tell you that females with long hair will wear it down when wearing a flight helmet. Look on the ground in front of her...that’s an HGU-56/P Flight Helmet. It would be unsafe to wear her hair in a bun or with any metallic hair clips as the flight helmet would not fit safely. Plus the hair clips would be a FOD hazard.

Judging by the plates on that VW, I’d say that they’re on Wiesbaden Airfield, so there’s a really good chance that they are adjacent to the flight line...probably conducting a crew and passenger pre-flight safety brief.

If they're on the flight line, or in the process of preparing to fly there's no reason for her to keep her hair in a bun. A bun cannot fit under the aviators helmet. Is it official that they can lower their hair? Probably not. But I see it akin to why we can't grow beards, it interferes with wear of equipment. So why correct her?

Yikes! Your troops and those around you are a direct reflection of your leadership skills and connection with those under your supervision or command. If she’s part of a maintenance or flight crews this seems like a safety hazard... but this Army so... anything goes?

I don't care who you are when that protective mask needs to be worn to save your life that excess hair needs to be Gone!!! That being said 'what's your excuse for being dead pilot?'

Swing with the Wing!