I"d offer her a pot next time she comes by...maybe just say you can't use as many of the "mature" i.e. rooted ones, as you first thought.

When we first moved in, a woman and her mother, who lived across the street from one another, brought us cookies and offered us as many day lilies as I wanted the next fall. I never was able to go get them, then and would feel kind of funny asking for the six years later.

There's no chance of anyone taking anything from our front yard as we have a picket fence all the way round. There's not that much out there anyway.:-)