I talked about the Trip Tunnels in Allen a long time ago and I know we can't talk about specific places that are or have been searched, but I hope they have been checked in to. I saw another website that was written by some guy who went "exploring" drain tunnels in the area, and it was crazy because he had pictures of them and everything. He only briefly mentioned Allen, but had a big list of others in the area. He talked about some of them expanding into huge room-like areas far back into them. I'm not sure how accessible the ones in Allen are, like if you could easily go from a car into them, but still it might have been a place to dump of her belongings or hide something temporarily. In Allen, I know that one entrance is off Bethany.
**Here is the link to the guy's site I had found before in case ya'll are interested. Some of these are creepy. I can't imagine people enjoying exploring these, much less partying in them, but in Allen they were known for that. I first read about them on an Allen fb page.
http://alexplorer.net/urban/explorations.html