Maybe try laying with her and gradually moving away once she is asleep? I think its 10 minutes after they fall asleep they enter a deeper state of sleep and then after 40 minutes they "lighten" up. So maybe put a pillow where you have been laying so that there is something there. I think music is a great idea too. Matilda has music in her room playing constantly so that if there are different noises in the house, she at least has some constant. ykwim?

Good luck! At 9 months they definately become more aware of things around them, so if they go into a lighter stage of sleep it may wake them up knowing you aren't there.