I would make it very unpleasant for Dylan to bite and mouth at your daughter. The problem is that if she squeals and runs away she is rewarding his behaviour, and he will give chase. I wouldn't say its a boss thing, and I wouldn't imagine he's taking any notice of her eating before him - you need to take things to a very basic level :)
I cured my Dane puppy of targetting my 3 year old this way - its very effective, but it must be done correctly.
Arm yourself with a squeezy water bottle (something that gives a good soaking though - not a water pistol, and a saucepan and a wooden spoon. Don't let the dog see you have these, hide them. Then as soon as you see Dylan going for your daughter run up behind him as fast as possible and whack the saucepan as loud as you can with the wooden spoon. He should sit down and wonder what the hell was that!!

Repeat this ONCE, then move ontop the water if he continues to reoffend - give him a good soaking in the face. It must be YOU who does this, your daughter should not be seen to have any part in it, and you should try to look innocent aswell.
The point in this is that Dylan learns that something unpleasant happens when he pesters your daughter - they learn fast - it took Willis 3 goes and he never chased Zack again :) Good luck.