I'm so sorry to hear about your service animal. That can feel like losing part of your own body.
A couple of thoughts -
1. I would go with something pretty, bushy, and easy to manage, such as gin berry (glycosmis pentaphylla). Unusual, beautiful, takes well to pruning, does great in a pot and grows well from seed. I have them coming up all over my greenhouse just from eating the berries and spitting the seeds out on the floor.
2. Remember, even if a plant fails, her ashes are still in the potting soil, ready to give nutrtion to whatever else you plant in there.
If you want some gin berry seeds to start, I have tons! Just let me know and I can mail you some when I get home on the 26th.
Cheers,
Carolyn