Is there any way you can get in touch with the former owner? I'm sure she would LOVE to know that her plants are appreciated and are being cared for.
If you don't know her address, her real-estate agent probably does.
Look back through your closing papers. If you don't have her agent's address, call your own real-estate agent and get the ball rolling:
Write a letter to her and ask that it be forwarded to the former owner. Include pictures, with questions written in pencil or non-smearing pen on the back. Ask whether she was actively trying to attract and support butterflies. (This will let her know that you have indeed been checking into the plants!
) You might also want to know how old the mature trees/shrubs are, so that when/if they begin to have problems down the line, you'll know whether it's likely to be disease, insect trouble, or end-of-life decline.
We kept in touch with the former owners of our house for a time, and the information was very helpful, since many of the plants were ones with which I was unfamiliar. We also had a professional gardener do a walk-through and identify some of the smaller ones and give us clues as to water needs.
It sounds like you've acquired a truly wonderful spread!
USDA Zone 9, Sunset Zone 17