There's an in game solution but it's a bit silly and tedious.
1. What you do is make the girl you want to move out the "main" household in the split household pop up. That means you move the parents to the right column (new household section). And then you move the parents out to an empty lot.
2. Then you put whatever stuff you want to the girl's inventory. Then you move her out and pick "sell furniture", so the furniture stays in the old house. Put her in a new house, etc.
3. Now, you can move the parents back into the old house. They might not be able to afford the house, but you can use the motherlode cheat.
Or what I like to do is merge random households to the parents' household. This will make the income go up. That is totally not cheating.*wink wink* XD And then move them all in to the house and then kick out those random sims.
But yeah, I think buying the stuff again is much quicker than this, but just in case someone wants to use this method to put personal stuff like collections, paintings made by the specific sim, etc, this is the way to do it.
