The best way to know if a foot will match a particular machine is to know if the machine is high or low shank. That is the distance from the pressure foot screw to the bottom of the pressure foot or to the needle plate. I suspect your machine is a low shank.
Low shank machines measure about 3/4" between the screw and plate.
Hight shank machines measure about 1 to 1-1/4" inches between the scew and plate.
Janome makes a convertible free motion quilting foot set that has an open toe attachment, a closed toe attachment and a saucer shaped foot. This foot set comes in both high and low shank versions.
Free Motion Quilting Convertible Foot set for low shank machines
I should add that I do not know whether this foot can work in the Sew Petite. It is a rather large apparatus as you can see from the link and it also cost about $70.
A more generic foot might work... there is a popular plastic foot sold by Clotilde call the Big Foot. It is for FMQ'ing and comes in both high an low shank versions. I think it is more affordable.
Another point about quilting on such a small machine is that it may be better for piecing blocks but to push a quilt through the harp area of the machine is another matter altogether. A mini machine means little space for quilting unless we are talking about doll quilts.
Janome MC6600, Bernina 240, Juki MO735 serger, 1948 Singer 15-19, 1950 221-1, 1951 201-2
10:42 PM by