Rosie is very sick

This is Rosie, she’s 13 and my best friend in the entire world. I always say she wasn’t supposed to be mine but we were always meant for one another. Originally she was my parents’ dog, but after my mom died and a falling out with my dad, I ended up taking her with me. At certain points in my life, I literally didn’t have anyone besides her. 3-4 weeks ago, she started coughing and we took her to the vet. The vet couldn’t find anything so she was treated for bronchitis. After a few days, she stopped eating. We thought the antibiotic was really harsh on her but after days of her not wanting anything at all, we took her to another vet. It’s a low cost humane society and they didn’t have all the tools we may have needed so we took her to an ER. That ER vet said it could be anything from lung disease, heart failure, pulmonary hypertension to cancer and more severe illness. We ended up taking her to another ER so she could see an internist where a lot of the same was discussed, including possible end of life. The cardiologist couldn’t find anything but we did get to take her back home. My fear was that we’d lose her while she was in the hospital as we also signed a DNR. Right now she’s on steroids, another antibiotic, and an appetite stimulant and we’re hoping we have her for a little longer. We knew she was getting older but she hasn’t showed signs of significant aging and this hit us all of a sudden. We haven’t been able to go on walks since the weather cooled down and I just wish I had the real her back, most of the time she’s sleeping and laying down. She’s the last remaining piece I have of my mom and I just want her to be ok :( I just wanted to share my girl with people who understand. I love her so much and, if nothing else, I want her to be comfortable when it’s her time to go to the other side.