Just a cut and paste off of studyguide. Unless something has changed or there's a Service difference I am unaware of ponytails are prohibited unless you are on your own time off duty PTing in civvies. A uniform is A uniform is A uniform. In three years I never saw a free swinging ponytail in a PT formation.
And the sock trick works great if your hair is not long enough for proper bunning. If you get white cotton toddler tube style socks you can dye them to match almost any hair shade. Experiment with the sock thickness/size for different diameter buns. IIRC, Basic teaches females nothing over 2" in diameter. If I had it to do over I would've cut bangs and my hair into a modified bob (top of collar/a little higher) when I went on Active Duty. Buns are a pain in the neck (literally, if too tight and pulling short hairs) and the no bangs/fringe is so severe looking. Well, on me it was anyways.
Female Hair Standards
Female soldiers will ensure their hair is neatly groomed, that the length and bulk of the hair are not excessive, and that the hair does not present a ragged, unkempt, or extreme appearance. Likewise, trendy styles that result in shaved portions of the scalp (other than the neckline) or designs cut into the hair are prohibited. Females may wear braids and cornrows as long as the braided style is conservative, the braids and cornrows lie snugly on the head, and any holding devices comply with the standards. Dreadlocks (unkempt, twisted, matted individual parts of hair) are prohibited in uniform or in civilian clothes on duty. Hair will not fall over the eyebrows or extend below the bottom edge of the collar at any time during normal activity or when standing in formation. Long hair that falls naturally below the bottom edge of the collar, to include braids, will be neatly and inconspicuously fastened or pinned, so no free-hanging hair is visible. This includes styles worn with the improved physical fitness uniform (IPFU).
Styles that are lopsided or distinctly unbalanced are prohibited. Ponytails, pigtails, or braids that are not secured to the head (allowing hair to hang freely), widely spaced individual hanging locks, and other extreme styles that protrude from the head are prohibited. Extensions, weaves, wigs, and hairpieces are authorized only if these additions have the same general appearance as the individuals natural hair. Additionally, any wigs, extensions, hairpieces, or weaves must comply with grooming policies.
Females will ensure that hairstyles do not interfere with proper wear of military headgear, protective masks, or equipment at any time. When headgear is worn, the hair will not extend below the bottom edge of the front of the headgear or below the bottom edge of the collar.
Hair-holding devices may be used only for securing the hair. Soldiers will not place hair-holding devices in the hair for decorative purposes. All hair-holding devices must be plain and of a color as close to the soldiers hair as is possible or clear. Authorized devices include, but are not limited to, small, plain scrunchies (elastic hair bands covered with material), barrettes, combs, pins, clips, rubber bands, and hair bands. Devices that are conspicuous, excessive or decorative are prohibited. Some examples of prohibited devices include, but are not limited to, large, lacy scrunchies; beads, bows, or claw clips; clips, pins, or barrettes with butterflies, flowers, sparkles, gems, or scalloped edges; and bows made from hairpieces.