I read to slowly bring the treat down in front or have her sit then slide her legs out to make her lay, but neither worked for us. When I try to grab her legs she backs up.
The couch idea would've been great to know.
I looked up other ways & had to just catch her every time she laid down saying "down" "good girl" repeatedly, giving the hand signal & even treating her. It did take longer than any other command but she did catch on.