Sometimes she will do it on command or she will just ignore me.
The dog thinks you're a putz and has better things to do than listen to you.
Lack of consistency on your part, training never stops, it should enforced on the daily basis for the life of the dog.
She likes to do what she wants
As long as there are no consequences for disobeying a command, a dog will. There's nothing in it for her and she is in charge and does as she pleases. If the dog is rewarded every time it obeys on the first command and corrected if it does not, it will learn to lie down on the first command.
It is lie not lay [ Quickanddirtytips.com Link ]
Probably she speaks English better than you and knows that you should be saying "LIE down," not "LAY down."
Because dogs don't generalize. Your dog doesn't understand that "lay down" means lay down wherever you ask. So, you teach her, that "lay down"is to be performed whernever you ask...be it the backyard, front yard, sidewalk, living room, school yard or stip mall.
Dog not ignoring, dog simply doesn't know the command well enough.