Our beloved 8 year old rescue greyhound was diagnosed with osteosarcoma 3 weeks ago. We thought she'd just hurt herself running as that's when the limp started. Vet couldn't find anything wrong and gave her an anti inflammatory but after a week of no limping it came back. Almost over night a lump appeared on her shoulder and the vet X-rays showed bone abnormalities that suggested osteosarcoma. She was booked in for a biopsy but before doing it they did a thorough examination and more X-rays and rang to say that they were convinced it was osteosarcoma and that the biopsy would be extremely painful as they would have to go into the bone and would potentially fracture the leg so they wouldn't advise putting her through it.
They also didn't think she was a good candidate for amputation due to her age and arthritis already setting in and would but her maybe a couple of months extra but be extremely distressing and difficult for her. Basically our only option to save her more pain and suffering was palliative care with a cocktail of drugs until we can no longer relieve the pain. 
She responded really well to the drugs at first and was back out walking and only looked slightly lame if you really looked for it.
However she went downhill almost overnight a week ago and despite trying two extra pain meds she's hopping lame. The tumour seems to be growing by the day as well. I'm sleeping on the floor downstairs with her as I'm terrified she'll hurt herself going up and downstairs. She's still eating and wants to go for short walks but it's so sad to watch and I'm scared she will hurt herself and it will mean emergency pts. The new medication is Amantadine, does anyone have any experience of how long it takes to work? She's been on it since weds night as the vet had to order it in. It doesn't really seem to have made any difference so far but I've read it can take a while.
I'm devastated but the last thing I want is for her to suffer. If we could at least get her pain under control until half term we could give her the best last day ever and let her go unhurried and grieve in peace. She's a bit sad sack but she perks up once outside and is still eating and responding to us, wags her tail when we come in etc. It's so hard to know the right time and if we wait it out will the medication start to work. Just want to do right for my girl but struggling with the reality of her having to go. The worst case would be her injuring herself and it being an emergency pts as our vet will only allow one of us to be with her due to Covid so we plan to have a vet come to the house when it's time so we can all be with her. Does anyone have any advice, experience or even just a paw hold? 