Keep a close eye on her. They will get very restless (usually) will go down to rest, but not really rest, the up again, then an hour later, back down again, etc. They also will have many poops that are (usually) very soft and will pee frequently.
When their bags get hard and start hurting, they really do not like anyone touching them there. I also find that if you continue to try and touch them there, they are more likely to give their foals a hard time to begin with too.
Maiden mares always scare me, as it is not always easy for them. My maiden mare just lost her foal this year. Other years I have had to really pull on the foal to get it out,( feet on the mares butt pushing with my feet while pulling on the legs. Though never pull unless the mare is pushing) One time the foals head was jamed into the pelvic bone and the poor mare had some nerve damage and could not walk right for a few days and for months, she cout not trot. Other times, I have had maiden mares foal out in the pasture when they have shown no signs of being ready to foal. Gotta love the maiden mares.
Chances are your mare will foal sometime tonight, but then, they have not read the book and could go on like this for days and even weeks.
Sorry, not much help, but theya re hard to predict.
Here is hoping your mare goes tonight and everything goes smoothly!