Tiny Steatoda laying eggsac!?

[CRX]

My house became colonized with Steatoda last spring, and I've seen some massive females. I have a pretty tiny one I've been keeping, nowhere near as big as the biggest females I've seen, and today I saw she laid a sac!! Is this normal for ones this small? Do they reach sexual maturity that fast, is this how they're so invasive? Because she really is small.