BY THE WAY. I think #9 happens when she's walking faster than you towards you straight behind you. So it's completely intentional. To demonstrate, put your speakers up to 100% so you can hear her walking...JK LOL, if you try that again you'll get treble boosted from the screamer, but seriously. She's a real quiet stalker.
(If you don't want to put your speakers up to 100% so you can hear her walking, constantly look back. If Marzia's within view though, she'll walk faster if you look at her.)
Also your angle always instantly changes when you're caught (except for in the ending of the Math Level). Probably to make it startling.