Hi everyone,
Thanks for all your replies. Gertrude has crossed the rainbow bridge tonight. We decided it was the best option. She looked way more declined when we saw her tonight than what she was like yesterday morning and that's with more medication, fluid and feedings.
The vet also did an x-ray again and both vets have looked at the results. The lungs were smaller and they found abscesses/masses in the tissue which is what's causing it. It is possible that this was cancer and was spreading.
My heart aches right now. But this was the right decision, especially when we saw her to say goodbye she looked like she was done and had tears in her eyes as well.