Lavender needs excellent sharp drainage to be a reliable perennial in this area.

Peonies will live forever. Roses are also a good choice. Lilies if there are no deer problems.

Is she local? Based on my yard, I would recommend peonies. Lavender doesn't work in my yard because the soil is too damp and clay.

A trio of perennials that bloom at different times of the year. For example, 1 peony+1 summer phlox+1hardy hibiscus. They require sun exposure.

Bleeding heart plants if her yard has a shady spot. They will come back every year and depending on the zone, might even bloom around Mother’s Day.

My mother loves hydrangeas, but it does require some pruning at end of the season.

What kind of light conditions does she have outside? And what size are you looking for? I would go to a garden store and see what you like. If she has at least some sun, maybe a perennial geranium or a salvia plant (spiky purple flowers) or something that blooms or looks good into the fall, like Paris coral bells (love mine - so pretty now but should look good in the fall).

I like ranunculus or lavender

My mom loves flowers, but she normally but annuals to plant outdoor. Please suggest one perennial flowers for me to get from stores as gift to add to her outdoor gardening in zone 7?