Here is a quote:
“I thought Mab’s wrath was pretty bad until I found out what her affection was like.”
Mab''s idea of sweet is 77 attempted murder. See how much she makes the effort to prepare Harry? She probably believe that if Harry really dies in those trainning attempts it will be the best thing for Harry ever.
Same withhiring him to find the summer knight mantle in SK and when Mab takes away Harry's fire magic in Smf.
Mab is just taking good care of his most beloved Harry dresden.
Mab believes in tough love.
I'm not saying Mab is all kind, sweet and lovey dovey with Harry. It is not in Mab's nature to be that way. I'm just saying she is nicer to Harry than how she treats others of his station. Look how Maeve was treating Slate. Mab was putting Harry in WK boot camp so he would survive confronting Maeve, her posse and the Outsiders. She was not trying to kill him. If Harry died in training it would be an easier death than in the field.