spoilers:end of spoilers
I think Agatha is interested in how Wanda made the hex and whether it can really be used to resurrect someone. When she killed Sparky and Wanda was consoling the kids, Agatha was particularly interested in whether Wanda could really bring someone back to life. Also, the questions Pietro was asking Wanda about how she did it all adds to this now we know he's working for (or being controlled by) Agatha.