I think it might have been better if she had put them both down together... Zak is really arthritic and thin, just like Zeke was, and I think Dona is just so tired of the ongoing stress of vetting first the cat, then Zeke, and now Zak. Zak will never be well. If I had been there, I'd have advised to put him down and get it over with. They both had good long lives.
You're probably right. But I could also see how it would be hard for her to do that.