An oral agreement (assuming there is no written contract) is enforceable, but it's only enforceable as per  its actual terms. So if the agreement was that she would display your logo and let you use it in your portfolio, you could possibly sue her  to enforce those terms--logo and portfolio. However, you could not sue her for payment or otherwise require her to pay, if that had not been the agreement between you--one party to an agreement may not unilaterally, or on its own, change the terms of the agreement, such as by requiring the other party to pay amounts which they had not agreed to be responsible for.