I'm pretty sure summoning Outsiders at all gets a mortal on Mab's shit list, but I don't think it's going to become personal to the degree that Slate's punishment for betraying her was because of what the particular Outsider did. Attacking accorded neutral ground is only really a personal slight to her if it's perpetrated by a signatory. HWWBh attacked Mac's because Harry was there, not because the summoner actually had power over it and directed it to do so. So she has no reason to apply the laws of the boss being responsible for the vassal's actions - if anything, the summoner is the vassal of the Walker, even if deluded enough to think he or she is in charge of it.
Mab would have the summoner killed if at all possible, but probably on a "it's just business" basis. Either Harry gets a straight up hit order, or the Wardens get a tip about the whereabouts of an outsider-consorting warlock.