Acquiring German citizenship by descent

My great grandmother was born in Köslin, Germany (now Koszalin, Poland) in 1925. My family were farmers, but lost their farm to the Russians during the war, and then migrated.

I am interested in applying for German citizenship by descent, but I'm not clear on whether or not I'm eligible, so I thought it would make the most sense to bring my situation to reddit so those who understand the process a bit more than me can tell me whether it's even possible.

My family and I speak German and we've always celebrated German traditions. We live in the UK (which does allow dual citizenship). I have a photocopy of my great grandmother's birth certificate, but not the real version.