Her vision of the Tyrell rose weed spreading its tendrils across Westeros is coming true!
Now she just needs to somehow intermingle with Dorne and the Eyrie and she'll have all the major houses covered.
I think Rowena was originally responsible for Jonelle's death too, but that was back when Jonelle was only connected to her through marriage because the original Stark mom was her niece by marriage. So I'll probably have to retcon that. I don't think she'd kill one of Gemma's babies.