Help me i need answers?

my poor rotti has just been taken to vets she was so sick an loads of blood coming from her back end and it was a lot im glad it happened in the vets she is still there on a drip she has always suffered with her tummy but never ever this bad she is well loved all vacinated she just had the all clear to go on walks after her cruciate ligament repair she was in vet wed to have x ray to see how her leg was and she has not been well since she came out im thinking she has picked up something up while in there im so worried about her she wes so ill anyone got any answers out there please