How do I defend against this claim and win if nothing I did was illegal or malice as she is claiming in her suit?

I recently sold an item on a Facebook rummage sale. In my ad, I had mistaken on the dimensions saying 16x20 in the item. It is in fact a 15x15 semi auto heat press. Upon meeting the women who was interested in purchasing the item, I explained that I had made a mistake on the dimensions, and was still firm on the price given that is the going price for that particular model. At the meet, we spoke for roughly 20 minutes as she had many questions on how to use it, and that she had many orders of t-shirts she needed to make for a local club. We exchanged product for cash $300, and I went on my way. Later that evening, she called me to tell me she found one online for $99. I explained to her that was a promotional thing on the website and she would have had to buy $300 worth of that sites products in order to get the heat press for $99. I also explained to her that all sales were final and that the Facebook rummage sale does not have a return policy. I feel as though the item was explained in being incorrect in my post on the dimensions, along with her having enough time to research the item. Now, I am being sued in small claims court from her for theft by deception. She was sold a brand new item with full functionality. HELP! I have never been sued in my life and am not sure how this is going to play out. I have printed all email exchanges, along with print outs of the item being sold at that value online.