Doesn't need to be deep at all, can be flat on ground and stapled down until grass grows back thru.
Good examples of anti-dig apron installation:
https://www.backyardchickens.com/threads/wire-around-coop.1110498/#post-17093528...
This is part of why you need to get the HC tight and taut and well attached.
If they can get a tooth in, it can be torn up.
Ask her permission then you could screen shoot it if she can't/won't send copies of the vid and pics.