First off, what a kind person you are, to even be giving this so much thought. Maybe a pretty little plant would good be to put on her desk, along with a small card saying "for you and ___". There is sure nothing wrong with a card showing you donated to some reputable animal rescue group, either.

If you can manage time, an invitation to lunch would be nice. Sometimes just the act of being there as a friend helps the grieving process.

I think she would appreciate the thought, as any pet owner would. Whatever you decide to give her, you should just set it on her desk and not make a big deal of it, as I'm sure she doesn't want to have a sob session at work.

Yeah the card and the donation are totally appropriate. It’s not over the top and thoughtful

I love that idea of a donation.

A simple sympathy card would be appropriate.

A new cat ? 🤔