The visual signs of a mare's readiness to foal are:
1.) Udder distension begins 2-6 weeks prior to foaling.
2.) Relaxation of the muscles of the croup 7-19 days prior to foaling; relaxation around the tail head, buttocks, and lips of the vulva.
3.) Teat nipples fill 4-6 days prior to foaling.
4.) Waxing of the teats 2-4 days before. Waxing (or wax beads) refers to the colostrum (first milk) which appears at the end of the teats.
5.) Dripping of colostrum 24-48 hours before foaling. Loss of colostrum may result in an inadequate supply for the newborn foal.
6.) Prior to foaling, the mare's body temperature will be equal to or drop lower than her normal morning temperature.
I was researching a little bit, and am only going off of a few of these that I have observed. Her udder has already filled an obvious amount, and she is very loose and relaxed. Her teats filled 4 days ago, so that is a check. No waxing, dripping, and I haven't taken her temp. Milk is still clear.
I think I am going to get a few hours of sleep before I go peek at her again.