I wouldn't hesitate to give the dog walker the bill, although your dog should also not be off the lead if you can't recall her instantly, but I do know what you mean about lurchers! I have 3 dogs, they are never off the lead if I see other dogs around, but like you I have been taken by surprise at times, one dog is never off his lead unless in a secure dog walking enclosure because he does come back, but only in his own sweet time, which is not good enough for me, the other 2 are fine, but are kept on leads if other dogs are in sight because I feel more in control that way. I would never walk more than my 3 dogs at one time, I fail to see how anyone can control 7 dogs on or off lead and the sheer strength of 7 dogs would pull over any person, it should not be allowed. I would definitely get in touch with the council re licensing, maybe the dog walker is breaking her license conditions and she needs stopping before a tragedy happens, if not a call to your local PCSO is in order.