Hi Alina
does the Josephine still have a stem or root crown? if there is a stem is it still green inside when you cut it?
if the stem and crown are dead and rotted then the chances of it coming back are slim but she may decide to push up another shoot.I would pot her up and when you put the roots in lay them at a slight angle this might help it to produce a new shoot from under the root crown.I worked at an all clematis nursery and plants that were thought to be dead were tossed into a soil pile.I would then sometimes find a rootball that had been buried and there would be a new shoot coming out.the thing that was interesting was the position of the rootball sometimes they were almost upside down and there would be a little white stem growing.I would say your Josephine has a good chance of being alive.

Hi Clematis_not_bombs,
Thank you so much for your answer. It did not have any stem when I got it. Neither my other bare root clems had stems. It does have a crown. I potted her back after digging up, but you gave me excellent idea to plant her at an angle. If it is weak but still alive it might help her. So I will repot her at an angle and see what will happen. I have nothing to loose, and if I will manage to get her back to life I will be very happy.
I appreciate your help so much, thank you!