First off, use something like flour or cornstarch. Baby powder has a smell to it that might discourage her from crawling through it and defeat the purpose.
Are you ABSOLUTELY sure she isn't in that crawlspace right now? If she is, you don't want to block it off and trap her in.

If you have a heat pad or lamp that you could place so that it warms an area of the floor near the tank, that would be a good idea. Also maybe getting a handful of her bedding so it has the smell she's used to. Keep the water near that. Also, thaw out a feeder and put it under the lamp as well. If she's hungry there's a good chance she'll smell it and come looking.

I might pick up the trashbags... I just have a feeling that could freak her out and cause her not to go near them. Most trashbags have a really mild perfume to them in addition to having a bizarre texture that the snake would find off-putting.

Also, when you put down the flour/cornstarch, keep in mind that they generally won't go out in the open, but prefer to crawl along baseboards and walls. Additionally, they generally will hide VERY close to the location of escape. That might help you narrow down where she's at.

Lastly, how are you securing your enclosure? Once you find her, it'll be important to make sure she doesn't get out again.