You bought her 2 days ago, she is probably still shy.
I am not a expert but i have my cockatiel for 8 years now, its also summer and that might activated molting so maybe she is little tired of molting aswell.
keep your patience, pay attention to her feathers and how she looks in general, keep her fed and give her enough water. If she is in the full sun give her the option to sit in the shadow, maybe try and shower her with a plant spray (on the vapor setting).
Dont go near her with your hands and dont scare her.