Growling over a toy?

I picked up some new toys for the kittens today. Lily is really obsessed over one- a glittery pom pom ball. As soon as she saw it, she picked it up and ran away to her "safe corner" where she's been chewing it and batting it around for an hour now. In the middle of her normal nap time. And she's growling almost constantly whether or not Eve is near her. If Eve tries to butt in, she gets hissed at.

Why is she growling over this toy? I've never seen her do that before, even with the similar-sized catnip toys that she loves. Lily is usually very mild mannered, at least now that she's over being food aggressive. Should I take the toy away? Or should I leave it with her and hope she gets used to it, the same way she got used to being fed regularly?

Mooch was that way with her 'baby doll' toy. I never took it away from her, Noodles just kept her distance from it. Now they are older and Mooch doesn't play with it as much, but Noodles still doesn't go for it. (I bought her another one that is her baby!) From what I understand, things like that can just be an issue of dominance, establishing themselves as the alpha cat. I'm sure someone will come along with more experience, but I wouldn't be too worried yet.

When I've had kittens, this wasn't unusual behavior at all. Sometimes it is hillarious to watch! I had a kitten (not mine, though) who was playing tug of war with me over a foot long piece of grass- growling and yanking just like a dog, except, if he weighed 2 lbs, I'd be shocked!

Sophie growls at a couple of the toys that she bats about. She sounds like a baby lion cub and it's so funny!

Thanks guys, that makes me feel better! I was worried that she might attack Eve or something, but she never did more than growl and hiss. She's been a bit lethargic due to a URI so it was awesome to see her play this much! She played with that fuzzy ball for over an hour and a half before she was too tired to play any more. Then she followed me to the living room and saw the second one lying on the floor and couldn't resist a few more bats and growls.

Mine have all growled over a favourite toy at some time or other! They also do it over a special treat or over something they have caught. Now, whenever I hear that growl I go to check what it is. Basically it means 'this is mine and you all better recognise that and leave me alone with it'.