If she's laying egg sacks, sadly, it's near the end for her. She's likely at her 7th or 9th instar stage just feed her, fed her as much as she'll eat, Mantids are great and they eat a lot! But don't be too shocked when "that day" comes. They generally live about 9 months ("instars" or skin sheds). Egg laying is a sign of old age for them. If she's a female that hasn't had a male partener each baby will be a tiny female clone of her. This is called "parthenogenesis" ( I doubt that I spelled that right)
When the babies hatch you'll have anywhere from 100-400 babies so pick a few as pets (keep them in seperate containers) the rest will have to go free or die at their brothers and sisters hands (blades) as they are cannibals.
Eggs will take several months to develop and then hatch. You can delay hatching by keeping them refrigerated (not frozen) the cool temps put them into "stasis" like cryogenics on an embryo. Then you can pull them out and let them warm up and they will continue to develop and then hatch when they're ready. I keep egg twigs (sacks laid on sticks) in a gallon jar with a screen lid ontop of my TV so I will see them as soon as they hatch. When they hatch I sprinkle the children out all over the garden to go where they may.
If you keep one in a cage, a net cage is nice because it gives them lots of "walking around": area - they don't need super high humidity. Just a cage with twigs and some plants to climb on. You will need to mist the plants every day so the Mantis can get a drink - they drink off leaves and such. Feed them small bugs - baby mantids need fruitfly sized food. Babies will run from ants since they are about the same size (1/8" or so) so don't fed them ants. Ants are sometimes toxic and can bite back with their big mandibles. When the mantids get bigger feed them small crickets and then large crickets, moths and flying things are appreciated too if you can catch them for it.
After you feed it for a while the mantis will "get to know you" and allow you to hold it and feed it by hand like a veiled chameleon, but they are skittish at first, your old maid wild one may never become hand tame but the babies-knowing only you, will generally be tame after a few months.
Have fun, Mantids are one of my faveorite insects - when they watch you watching them, you just
know they're thinking something!