My kids are all very slim, which makes buying pants very difficult. Any pants that have any chance of fitting them in the waist are *way* too short, even though my kids aren’t particularly tall.
I look very closely at style. Even though girls’ pants are often not labeled as slim, styles in which the pants are intended to be very tight fit my kids better. I buy pants that are the right length and then I alter and take in the waist myself. This is the easiest when the pants have an elastic type waist, like most athletic-type pants (leggings, yoga pants, etc.). You can add elastic to pants with a button-waist like skinny fit jeans but it is more difficult. The waist cannot be too big, or it looks weird even with the alteration.
In general, I have found it easier to buy boys’ slim pants. Lands End has boys slim pants with adjustable waists that you can specify the length. I buy these for my boys. My dd sometimes wears the boys’ outgrown pants when she needs dressier pants. This may not work if your dd is older and has hips, but so far, it works for us.
Otherwise, I end up having dd wear skirts and dresses for more formal occasions. Lots of skirts for kids have elastic waists that I can easily alter and dresses have no waist at all to worry about!
Good luck finding something!