How can I place a lien on someone either against their assets?
We cannot give legal advice, and are not forming an attorney-client relationship with you. The following is not a substitute for the advice of a local attorney. But we hope the information will be useful.
You cannot place a lien on someone in this situation. Liens are for work done. Not for simple debts. Small claims court may be an option for you - sue them for the debt. You will have to do it yourself. Not enough money to interest an attorney. Small claims court will have a complaint form to fill out and file. But you need to have some evidence that she owes you the money besides your word against their's.
The best advice is to stop paying for their cell phone.