If she seems to be straining but isn't pooping and doesn't have gas, then I would call. Colton became really constipated once and it hadn't even been a whole 24 hours since his last go.
However, with her being sick--if she is eating less she might not go as often. Colton will sometimes skip days if he isnt eating as much.
After the first 1-2 weeks they start pooping alot less too though, and she will probably get more into a routine, so it will be easier to notice if she gets constipated. Colton usually goes 1-2 times and 99.9% of the time it's always before noon.