If it involves curls, Mattel dolls will never match the promo pictures! I saw a Youtuber gave this doll a boil wash and she looked very good with a straight high ponytail. She also has a center part!
But I am surprised at the posability of your doll. My doll can strike that pose as all my MTM dolls.
Sometimes the joints are very stiff right out of the box, so you need to bend them with a little bit of force to get them flexing as intended. MTM dolls are quite sturdy so don't be afraid to move them. Good luck.