I'm a buyer in contract for deed for the last 10 years. I'm moving and either need to give house back or sell. I need to find out more about the options. She has a mortgage on house.

It all depends on the contract. Each is different. I have sold many houses and the contract did not allow the buyer to sell. But many do. Others may have penalty for early payoff.

If you merely walk away, what (if any) additional penalty would you pay?

What is the balance you owe (your payoff) to what you believe the house is worth.
Considering real estate fees, closing fees and the such.

I would often buy a house on contract, fix it up and then sell it for profit. But I always made sure my contracts allowed for this.

Another key question is how much the property is worth now and how much you still owe?
You bought pre-recession and many values still aren't back to what they were then. But you have put 10 years of payments into it. So sit down and calculate what is what.
If you want us to, you need to give us all the details.