@mantiscat If you can get a photo of the suspected egg sac I can help identify it for certain (a LED flashlight shined on the other side helps make the eggs visible). I looked through my photos and did not see one to show you (I guess they are all still backed-up, I'll have to dig them back out sometime).
The eggs though will be clustered generally in the middle of a web nest itself, and if against the side of the container appear orangish in color and oblong. If she mated before being kept as a pet, like most arachnids she is able to carry the sperm until she is ready to use it and lay her eggs.
I have kept dozens of Phidippus audax, Salticus scenicus, and Platycryptus undatus jumpers from everything between eggs to old age.
The odds that her egg sac is fertile is extremely high. The eggs hatch in about a month after being laid, at room temperature. I leave my mothers with the eggs (they keep them rotated and otherwise properly cared for) until they hatch and the spiderlings get about a week old.
You will know when they begin to hatch as the mother will flee her nest and stay outside of it until they have all nearly hatched. While the mother is gentle with her babies (and I have not seen cannibalism to them at least until after the first few molts), the mothers typically become annoyed at the sheer amount of them taking over the habitat.
At that point I move the babies to individual 2oz cups. For feeding spiderlings I give mine a mix of springtails and Melanogaster fruit flies, which they eagerly eat by scavenging the small dead prey.
Here are a couple photos of one of my Phidippus audax mothers spiderlings. The first is shortly after hatching inside the nest before it crawled out, and the last is one a day after hatching I got one to pose on a penny for scale.