First of all thank all of you guys for answering!
here is more information (the answer to the questions Imbrium asked)
~she is housed with another male rabbit
~She is 5 months old and stitch(he cage mate) also 5 months old
~Flopsy(the one losing the fur) is obviously a girl and Stitch is a boy:/
~ Stitch is fixed, he was fixed two weeks ago and Flopsy is not fixed
~they are properly bonded( they were raised by the same mom but aren't siblings
~I found the first clump of fur about 4 days ago
~I haven't seen ANY signs of fighting not even grunts they cuddle with each other constantly
~I believe the fur is coming from her neck or armpit areas
Sadly there is a possibility she is pregnant just because for the first month and half that I had them both I thought and was told they were both girls so there was no rush to get them fixed. One more thing I want to say is that the reason that she isn't fixed is because the vet didn't want to do an operation on such a small bunny but that was a month ago and she has grown a lot sense so we will get her spayed ASAP. That is if she isn't pregnant:/