This is one of the reasons that I would never leave chicks in the incubator for prolonged periods of time, (over 24 hours). While yes, in theory a chick can survive off the absorbed egg yolk for up to 3 days, we, one, do not know when the chick fully absorbed the yolk-according to the Cobbs development chart this usually takes place between day 19 and 20, which would mean those that do already are useing that source. And you also have to consider the possibility of dehydration that takes place during hatching. I like mine to at least have the electrolyte enhanced water and food available and then if they are not ready to eat- no foul, but it's available. Almost all of my chicks are at least drinking within the first 24 hours, a good share w/in the first 12. Eating is hit or miss. I get some that are pecking and eating in the first day and some that really aren't interested until the second day.
Glad to hear that she is doing better.