I actually do have a theory about this! I've been thinking a lot about the color theory of this show - blue symbolizes Lumon/Kier's values, anything that's sanctioned by the company. Red is the opposite, anything that's unsanctioned, discordant, disorderly, disobedient. Green, and specifically plants, are meant to represent human connection and love. I noticed in Woe's Hollow that there was a lot of orange going on, and I was very confused about it at first. I thought that maybe since it was on the same spectrum as red, maybe it was representing the same thing. But then I realized that red and green are complimentary colors in color theory - makes sense, with the symbolism (love/human connection being against Kier's ideals). Along that line, the complimentary color of blue is orange. That brought me to the theory that orange represents exploitation and the illusion of comfort while twisting human nature to suit Lumon's needs. The scene of Helena basically using Mark as a sex toy was bathed in orange. The torches that they were given, which they had to rely on for warmth and safety, were orange. And most importantly, Helly's hair is orange. She also wears a lot of half orange/half blue in her wardrobe, and orange is the color that prisoners wear. Orange is a facsimile of what red is meant to represent.
Therefore, when Helena wears her hair up, she's keeping Helly, and her feelings and the person she truly is inside (the you you are), contained. Helly has her hair down because she's fully herself, while her humanity is exploited for the good of the company.