I'd give HQ a call to see if you can use the quilt from the back kit- I think they did away with the conversion kits for the Sweet Sixteen that would have turned it into a Simply Sixteen for frame use so it might not be so easy to add the quilt from the back kit to your Tiara. Do you have your Tiara on a top carriage as well as a bottom carriage? If so, there may be a set of handlebars available for your top carriage.
Rob