I am jain, I love one girl from our caste ,her mothers family surname and my mothers family surname is same?

Now I was was not knowng her until I met her , she is not related to me , yet everyone is sayng it will be like brother sister marriage! Also people talk about genetic problems due to blood relation . We don't know in which generation we were related ! So how can we be relatives? The test for genetics is very painful! We are not first and second cousins!
Or is there really a problem in genes !please help me out