Dog stomach problems / possible tumor

[BoXx]

Our dogs stomach as been getting larger, to the point she looks pregnant. She is fixed and there is no chance she is pregnant. The stomach feels rock hard, and as it's growing she's having troubles with stairs and getting on/off the couch. Her spine is also starting to protrude from her back. 

 

I cannot afford surgery for her and she's been in the family 12 years and we don't want to put her down if we don't need too. She still wants to play and have plenty of "life" or energy. The mass just seems to be the only thing slowing her down. 

[BoXx]

this is her laying down. 

Just wondering if anyone has seen anything like this, or knows if surgery/putting her down are the only options as I have not been to the vet yet.