THANKS FOR YOUR WELCOME,
[I ALREADY NOTICED I MADE A MISTAKE IN THE WORDING OF MY REPLY].
I LOST BOTH OF THEM TO A CANCER THAT GIVES ALL THE SIGNS OF BLOAT, THE STOMACH FILLS WITH BLOOD AND THEN IS GRADUALLY REABSORBED - UNTIL NEXT TIME...
IT WAS ONE OF THE MOST HEART RENDING THINGS TO WATCH...
I am new to any type of forum so I am not speaking out of turn, but I have recently lost 2 of my beloved gsd,s with symptoms similar to that you describe. I won,t go into detail, but I beg you to have her checked by a vet.