Surrender or euthanize my 12 year old, sick dog?

My almost 12 year old dog (Pitbull/ Aussie shep mix) is severely anemic. We've been through months of expensive treatment, blood transfusions, emergency hospital visits, harsh medications ect...

She's been declining over the past month to the point where she can't get up off the floor on her own, and will only tolerate being outside long enough to poop.

We got bad news from our vet visit last week and made the hard decision to put her down next week.

Our vet called after hours last night to give us the option to surrender her to them, and they would proceed with further testing and treatment, that we just can't afford anymore.

The vet is now closed for the weekend lol so I can't call them to ask any questions, and we need to decide by Monday.

Has anyone been in this situation before? We're concerned that she'll be put through unnecessary stress, and testing, just to die anyway, surrounded by strangers. BUT if she does have a chance, I don't want to end her life just because we can't afford any more treatment.