in: wear or be wearing

Teo1. The girl in a red skirt is Tom's classmate.

2. The girl who is wearing a red skirt is Tom's classmate.

3. The girl who wears a red skirt is Tom's classmate.

What's the difference in meaning between the above three sentences?

No difference.

2-->wrong
it is odd to say wearing.
1,3-->the same.

I am a beginner too,dont believe me too much!

2 and 3 may mean the same. 2= now, or usually -- conveys aspectual meaning: annoyance; 3 = now or usually -- neutral.
1 refers to the present situation: at this moment.

It is my take on this.

#3 says that she wears it either all the time or often enough that you notice it. You may not be looking at her right now, in fact, but you know of her because she is the one who wears a red skirt so often that you know which person you are referring to.

I see no difference between #1 and #2. I would assume that you can see this girl and are using the red skirt to identify which person yo