A tweed is great! Unfortunately women's and girl's clothes are primarily made without much in the way of pockets, which we need. Nor are skirts necessarily cut to permit the long stride required to show giant breed dogs! Pockets are key! Treats, slobber towels, comb or brush etc. have to go SOMEPLACE.
One error I made that I want to share so you don't do the same dumb thing I did: It was an outdoor show in S FL, miles west of the coast. (are you hot and sticky just reading this yet?). I selected a polished cotton (chintz type of fabric) short sleeve peplum jacket and skirt suit to wear. I figured between the short sleeves and the cotton fabric this would be comfy. This was all true HOWEVER: what i failed to consider was the jacket ( a good quality suit) had an acetate lining and it was the hottest thing I have ever worn! The lining doesn't "breathe" like the jacket itself does, and I might as well have worn a plastic garbage bag as an undershirt!
Another gal I know reccommends shoes which tie. She was showing outdoors one time, in rainy weather. Her slip on shoe got stuck in the mud, without her foot, and somehow, in the judges' kindness, he assisted her to get it back on, getting mud on his clean suit in the process! From then on, every time he'd see her at a show, he'd call her "Cinderella" with a big, warm smile.
Always wear a color to contrast with the dog. If, for example you are showing a black Newf, don't wear a black outfit.
The majot problem is getting pockets and a skirt you can move well in. The better thrift stores (such as a Jr. League Thrift Shop) are good places to shop. I have trouble, anyway, being a size 2!
Best of luck to you and your daughter. I hope this helps
Mickey