Whether or not you move up from paddock boots to tall boots depends on the age of the child, whether she's on a horse or a pony, and the division she's showing in. These days, it is very, very rare to see jods and paddock boots on a rider on a horse, thought technically there is absolutely nothing wrong with it. I do agree with the comment that garter straps are a must if wearing jods.
I used to tell parents that when kids moved out of training bras and into a real bra was the time to move to tall boots.
Something disconcerting about pigtails, paddock boots and boobs.
Her clothing sounds fine to me. Hunter classes are conservative, and it's best if you stick with traditional, conservative colors. A plain, white, long sleeved shirt is fine, as is a subtle pinstripe, or a light blue, pink or gray.
I agree with the comment about the helmet and helmet cover. Also, if showing a pony, and in jods and paddock boots, pig tails are fine. If showing a horse, or in tall boots, hair should be secured neatly in a hair net. PLEASE invest in the best quality helmet that you can afford; not something to skimp on. It's a great idea to have one helmet for the barn and schooling, and another for showing. Keep the show helmet packed in it's own case or box; and wipe out the inside with a disinfectant wipe at the end of the show and before putting it away; it keeps the lining from rotting.
If she's showing in Jumpers (as opposed to Hunter over Fences, I wasn't sure from your description) her clothing is still fine. Other riders will be wearing brighter colors and flashier oufits, but tan jods and a navy jacket will cover most riding situations she's likely to be in.
Later on in her career, you'll hear a lot of discusstion about what colors look best on a bay, gray or chestnut, but I wouldn't worry about it for now.
Good luck, and Happy Show Season!