"I do not like this dress but I wear it."
Translation:Nie lubię tej sukienki, ale ją noszę.
Well, the thing is that we don't consider it "it" in such a sentence. "ją" is a declension of "ona" (she), it's just that English uses "it" here.
I called it a 'something like a feminine form of it' because it seemed to me like a good way of explaining how it works. But technically it isn't.
You won't say "To jest sukienka. Ona jest zielona", you won't use 'ona' to refer to a feminine object, but in other cases than Nominative, you will actually use other cases of 'ona'.
That's an interesting topic. I think 'she' is quite commonly used with boats/ships.