I think we may have different ways to explain this special and less-informal structure.
My way: the original full sentence should be 如果我穿这条裙子好看吗？
Colloquially, 如果我穿 becomes a less-important additional information, so the sentence becomes 这条裙子，（如果）我穿，好看吗？ "This skirt, (if) I wear, looks good?"
She could. But it is still more natural for her to ask 我穿这条裙子好看吗？ (no 的)Whereas if she has already put 'this skirt' on,she could`ve said:
According to this rule, 得 can show the degree or the result of an action.(3) 用在动词或形容词后面,连接表示程度或结果的补语。如:冷得打哆嗦;笑得肚子痛.
兵士凶, 她更凶, 凶得人家反笑了
The last two sentences are not grammatical. 你说得很对 should be 你说的很对. 你说的很对 means 你说的话很对.
As for 她穿(着)这件裙子好看 - 'She`s wearing this skirt now,and it looks good' - but I`m not sure WHAT is good,the skirt itself or the way she`s wearing this skirt.
I think I incline toward the latter.
In normal order, it would be 我穿这条裙子(的话)好看吗I`m a little confused about the formation of the sentence