I am not one to take things lightly and am very proactive by adding fluids where ever I can. While her system is probably slow to reboot, things I do to ensure things are moving along......
I like soaking hay, making a warm mash out of the grain (granted that it is pelleted feed, you can get away with 1/3 pellets to 2/3 warm water, usually fluffs up after 10 minutes). Well soaked alfalfa cubes work well too(make sure you break them up, sometimes the water is slower to reach the center. Make sure she has salt and mineral blocks aavailable to her, even if you have to place them above the foals reach. Any of these things will not upset her system, it is just a way to get more fluid into her. Don't forget, if the foal is nursing well, it is drawing fluids off of her, making sure she is taking enough fluids in to compensate for that is always important.
Keep an ear on her for gut sounds too, they should be increasing in sound as her system boots up, not decreasing.
Edited to add, I also do what copperwood farm listed below, as well as probiotics, but I usually use the above protocal first, then if there isn't any manure within 8-10hours after foaling, I get more aggressive about things by adding some oil and probiotics as well as possibly adding some electrolytes. Great information here.