Araneus marmoreus
(Marbled Orb-weaver)

And this is very likely to be a female. The females live about 1 year if you include developmental time in an egg. That begins when the eggs are oviposited and simultaneously fertilized in Autumn. When the females create the egg sac they guard it as long as they can. Where we live, the killing frost will take her around October.
The eggs are free-resistant.
Yours is close to making her eggsac or she already has. Males overall have shorter lifespans.