HI Barbara, I think it is a very thoughtful gesture. But I would also try to observe and consider if your sister in law is the type that likes to grow plants.
I would consider plants in a container, so it is easily moved as needed when seasons change. Or find low light easy to grow plants like Dracaenas, ZZ plants, Sansevieiras, Scheffleras.
Ficus microcarpa ginseng is also a nice tree, I got it as a bonsai and so far it is easy to manage, stays evergreen, slow growing. Just have to keep it indoors during winter by our south facing window.
