Second Opinion (of sorts)

"The mast cell tumors may return and she is a senior dog for her breed.

If the traditional treatment is totally out of reach for you then that limits your decision to trying the drug trial or doing nothing.

If that is the case I'd suggest considering the drug trial. It is possible the drug trial would not help her. That doesn't put you in any worse situation than being unable to treat her.

I'd ask and consider the possible side effects being seen (if they will tell you) to determine if the trial drug might make her worse (they may not tell you actual effects but might tell you if they think the dog will become worse in any way).

If the treatment is going to reduce her quality of life then you might not want to do it. But if it won't compromise her life quality and might help then it may be worth doing.

I hope I've helped you sort out some ideas on this. Its not an easy choice!"