My question is this, she moved out on her own, she owes me 400+$. I told her the next day after she moved she needed to take her stuff along with her. She said she would get it once I found a new roommate. I have found a roommate and let her know to come get her stuff. She said I gave her short notice and will not pay up. What can I do if she didn't sign an agreement?

Unfortunately you can't just toss her stuff to the curb, even if she owes rent. Nor can you take it to defray the amount she owes. You have to wait for it to be abandoned property, which goes by local ordinance (usually 30, 60, or 90 days) after you give written notice to take it away. You can (and should) send a bill for what she owes you, you can add X dollars a day for storage starting a week from when you mail the letter, you can put the stuff in storage for 1 month in her name and let it expire there, and you can sue her and she can sue you - and so on. Winning in small claims doesn't even mean someone pays.

Your best bet is to pile it all in a corner of the living room and consider it a lesson in roommate contracts for next time.