"She wears underwear."
履く(はく) is the verb for wearing something on your legs or feet, down-up. Trousers, skirts, shoes, socks etc. The polite masu-form of that is はきます.
着る (きる, masu-form きます) is for wearing something around your torso, so these are not interchangable. There are other wearing verbs for covering your head, tying around your neck, or slipping on your fingers/hands (or putting on miscellaneous accessories).
it gets a little confusing; first, the japanese forms we've been learning are not the present tense. -------います means "i do ------" (in general) OR "I will ------"
if you want something being done presently, like i am doing right now, it would be -----ています.
now, as far as the difference, they have different verbs for "wear / put on" depending on where it is. Like skeegenin said:
履きます（は・きます）is i will put on (for below the waist)
着ます（き・ます）is i will put on (for above the waist, such as a shirt, but things on the head have a different verb)
you haven't learned how to say "i am wearing right now" on duo, they haven't shown us those versions.
they are in fact the same word. 彼 (か~) means "he" and 女 (~じょ) means "woman/female"
EDIT: wait you meant that somehow かれ + ぬう = かのじょ, didn't you? I can see how that could be confusing if you don't yet know about onyomi and kunyomi readings of kanji. Unfortunately I can't really give any advice beyond researching the onyomi and kunyomi for yourself.