I agree with Mr. Ashby. If you do decide to go to small claims court, it would help to organize your case before hand. You would probably benefit from spending an hour with an attorney, although for such a small amount this may not be worth the money it would cost. You need to sue the person in the county in which they live. In addition, you can consult the following small claims court resources.
Good general advice
1. Everybody's Guide to Small Claims Court, Includes tips by former judges!, by Ralph Warner, Attorney, March 2012, 14th, Edition,
2. An Introduction to Small Claims Court, by the Washington Courts,
3. Small Claims Court in Washington State, August 2011, by Northwest Justice Project
King County Small Claims Court (if they live in King County)
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You likely can sue on such a verbal agreement, but if you have text messages from her then the agreement is most likely written. You can sue on your own in small claims court for up to $5,000, including for court costs. Go to your local district court and ask for forms. Good luck!
This answer does not create an attorney-client relationship and is intended to be a general statement of legal principles only. It should not be relied upon for any specific action. Please seek the advice of a qualified local attorney to review your specific case.
It sounds plausible that you may have a cause of action. It may be hard to find an attorney to take this type of case so you may want to consider filing a claim in small claims court. Good luck!