Kirsten! That certainly was scary! Glad she didn`t get to far and is ok!
Maybe if she gets scared when is comes to going down the stairs, if she gets out again, she will only wander upwards, which could be better than wandering out the door on the streets, and also you would know where to look. The stairwell sounds scary, does it have open staves or is it blocked in. Open would mean she could peer through and not jump on the banister, blocked in would be more problematic I guess, push come to shove maybe you could try some sort of netting?
Anyway, I`m hoping she will not make any more escape bids but stay safe and sound inside with her miowmie instead!

Chris