M.O.
NW,
I'm sorry to hear you're having such a tough time. I imagine it must be frustrating to have such an ungrateful, unappreciative child in the house. It sounds like you hit the nail on the head tho that part of the reason she doesn't care about losing things is because people keep finding them or replacing them for her.
What about a meeting with her Mom to discuss some "tough love"? Obviously this would have to be mainly between her dad and mom, but you need to be there to so that it is a collaborative effort.
I think she needs to "earn" privlidges such as ipods, cell phone usage, etc. The next time she loses something, she has to earn it back and definitely does not get a new one or new anything else until she proves she'll take care of it. Does she get an allowance? How about something in the allowance about helping out around the house (i.e. keeping her room clean and belongings picked up) AND doing some basic chores. The next time she wants something she needs to save up to buy it herself or wait until her birthday or Christmas to get it...isn't that what we had to do?
The more "stuff" she has the more inclined she'll be to not appreciate it. The more her things are replaced the less she'll be worried about losing it. And if you, dad, mom, etc. keep nagging her, she'll just lash out at you. If she's big enough to have all these expensive "toys", then she's old enough to deal with the consequences of losing them.
Take the "fight" out of this issue. Use logical consequences. Just make sure all the grown ups are on the same page first so you don't look like the mean one.
If/When she comes complaining/bawling to you about the next lost item don't be mean or insensitive, simply say, "Gee I'm really sorry you lost that/forgot to bring it. Have you tried looking in the place it belongs?" Then, that's it. It's now HER problem that you didn't create, you don't have to fix and you aren't nagging her about. If she continues to whine about not having it remind her that SHE lost it/didn't bring it and that's just too bad. (Just keep the mindset of "not my problem" without coming off as holier than thou. Be genuine, "I'm really sorry. That's too bad. I guess you'll have to find something else to do right now/some other way to entertain yourself."
I think the key is making a united stand with the other grownups in her life. The general agreement HAS to be "this is not OUR problem".
Good luck - let me know how it goes.
Sara