We found that a big plastic mat on the floor and putting the food on there that DD would come and eat when she wanted to, she now sits happily in a highchair I think they go through phases, another friends little girl has refused from the moment she could crawl, they woul put her food on a plate on a coffee table or chair and she would come and go as she pleased

She at a lot more that way rather than forcing the issue, glad the infant seat is working atm I think being a parent teaches us a lot about thinking outside of the square and flexibility