Before Twilight had kids she tried to relentlessly uphold the princess/alicorn appearance with the long (nuisance) flowy hair and tail, a goatee and no glasses rendering her squinting half the time. However that all changed when the kiddos were hatched and Twilight realized that magical flowing hair can be a magnet for grabby claws and teeth and that she also needed to keep a sharp out for their shenanigan.
As such Twilight decided to throw away her princess-looking image and excepted her mom haircut and glasses. Although she's till salty over the loss of her goateee. Discord knows how much Twilight reveres Starswirl and any way to illuminate his image is a win for her so he's finds it quite funny that she had to shave it :D (Big Grin)
However even the lord of chaos isn't immune to grabby claws in span of two weeks…he shaves his goatee as well. (ps. he also trims his mane as well)
Twilight's just glad their both stuck in the same boat now.