What are the rights and liabililties of a small business owner?

My friend runs an LLC of which she is the sole employee. She does freelance engineering design, mainly fire protection for fire protection companies. She does much of her work with other small companies without signed contracts. One has decided to not pay her for services rendered. Does she have any recourse to recover these monies.

Also, the same company has decided to backcharge her for additional expenditures they had to incur because of the approval/installation process (company occasionally installed prior to full approval by all applicable parties and now has to replace some heads). My impression would be that she was hired to provide a design document and it was the other company's obligation to approve that design and/or make sure it receives all necessary approvals. My belief is it is just a scare tactic to try to get her to back off of her demands to be paid. Again, probably would have been best to work with signed contracts, but it's too late for that now.

Opinions?

it would depend on the services that were agreed to, if she performed all of her duties as stated in the verbal agreement then she is entitled payment and should not be subject to any additional charges.

The difficult part will be to determine what was actually agreed to, she most certainly should have had a written contract and hopefully in the future she begins doing so.