一人の彼女 versus 彼女の一人

Question

Sometimes I find

一人の彼女

but sometimes I also find

彼女の一人

Is there any difference?

Answer 1

I strongly recommend you reconsider before saying 彼女の一人 to your girlfriend, because [noun] の (word means one) means one of [noun], so you're saying "one of girlfriends".

cf. 自転車の一台、手紙の一枚、動物の一種、空き缶の一個、部屋の一つ

Conversely, 一人の彼女 is only a counter counting the noun, that means "one girlfriend". Your girlfriend might well be pleased with this one.