“the reason for the pony tail”
My daughters school says it is to help keep lice and nits in check, in case one of the girls were to come to school with it.
As for dancingmom and her/his (why assume) sources. At the end of the day, the gemara in sanhedrin very clearly states that a womans “peah nachris” is just another one of her articles of clothing. Just like a woman must be careful in the clothing she wears on her torso, so to must she on her head. If your way of controlling the clothing you wear on your head is to simply avoid certain types of clothing, go for it. I for one wont tell you how to conduct yourself in this area, and in fact, encourage you to do whatever you feel you must do for yourself (along with healthy input from your rav and spouse, not necessarily in that order). please do not impose your hanhagos on others, especially if they are following legitimate halachic sources.