Sorry about the divorce, Bobbi. I agree w/ rosecarmel, I understand your feelings, but I would wait to change anything till the dust settles.
Not sure if you're saying you don't want to pick up GD from school at all anymore or only when she's w/ your DS (dear son). As much as I get how you feel, I think I'd want to help keep GD's life as "normal" as possible. She will be going through plenty of changes as it is. Your picking her up four times a week, whether it's "mum's week" or "dad's" may be one of the few constants in her life. Please think about that.
I know you're angry at DIL and want to teach her a lesson about "the real world." And maybe she'll accept the change as part and parcel of the divorce. Or perhaps she'll be angry in return. But how about GD? You say for years, she was w/ you more than DIL. If you drop her now, she may be deeply hurt. Is it worth it? Only you can decide.
In time, DIL may decide to pull away from you, especially if a new man enters her life, and/or as GD gets older and doesn't need anyone to pick her up. Then you'll definitely be free of that job (and may miss it). Perhaps you should enjoy the time w/ GD for now? Again, only you can decide.
Whatever choices are made, I hope it all works out for the best.