Thank you EVERYONE for you very kind replies.
I was just at the barn and JUBILEE IS BACK TO NORMAL. She's pooping (A LOT), eating hay and just being her usual normal self. What a difference from yesterday, I guess something just clicked.
And Brittany, it was impaction colic.
As for the grain, she seemed very very upset not to get fed any today. Lol. I brought her in the barn with the other horses but just gave her hay. Whenever I'd come near her she'd be nosing me for food. I felt so mean, but I didn't feed her any. I did give her a little handful and a carrot later on though.
Anyway, so today's Tuesday, so I made a little schedule for her grain rationing:
Wednesday AM/PM: quarter can
Thursday AM/PM: half can
Friday AM/PM: three-quarter can
Saturday AM/PM: full can
I am considering lowering her grain to three-quarters or even half. I do agree, she isn't getting worked enough for all that grain and perhaps that could have caused the colic since it was just sitting in her gut she wasn't moving much. She was stocked up as well.
I am just soooooo glad she's okay!!
Yay..... chips & salsa for the humans and treats for the horsies!!