Do I have to file a lien before she sells or is there anything I can do after she sells the home

If there is a payment due from the homeowner, you have a right to file a mechanic's lien for that amount. I would definitely recommend filing the lien on the property you performed the work on before it is sold. If you file a mechanic's lien you should get it served quickly and make sure the owner is on notice before the property is sold. The lien can work to interrupt the sale of the property, which will negatively impact the homeowner, which may positively impact your chances of getting paid quickly.