I don't have this one on my data base, but I did a quick search for you, and found this site. It does not mention that the roots are poisonous, so I think some more searching is in order. Over to you!

Here is a link that might be useful: hollyhock

I saw that episode too and what she called French Hollyhock, I have in my garden and it is called Malva zebrina. Blooms forever and is very lovely! Self sows freely.

That's fascinating. Did she say what part of the plant she feeds to her cats? Leaves, roots, flowers, fruits (which are called cheeses)? I have Malva sylvestris forms including 'Zebrina' naturalized on my place, and I grow Malva verticillata (one of the oldest domesticated plants) as a vegetable in my garden, but I never heard of feeding it to cats. My cats certainly don't show any interest in them in the garden.

You eat the flower petal and the immature seed pods. They are mucilagenous and soothe the stomach. Great for people with ulcers, similar to aloe vera.