You might want to make the strap long enough to go across her body,
this does have a tendency to want to slip off her shoulder.
I used regular worsted weight yarn and an H hook, my hearts are a tad less than 3".
To make a pillow simply add a little stuffing (or a few cotton balls) and sew it closed. Maybe add a white single crochet border, could be pretty...
These cute hearts would make a great garland or ornaments too!
Make a magic circle. There's a good u-tube about how to make the magic circle HERE.
Round 1~ Chain 2, 15 DC into ring, slip stitch into top of first DC.
Round 2~ Chain 2, 1 DC into same stitch, 4 TC in next stitch, 2 DC in next stitch, 1 HDC in the next 4 stitches.
1 DC, 1 TC, 1 DC into the next stitch (makes the point of the heart).
1 HDC in the next 4 stitches, 2 DC in next stitch, 4 TC in next stitch, 1 DC in next stitch, Chain 2, slip stitch into same stitch. You can stop by Crochet Leaf to see how to slip stitch from the back so the heart looks neater.
Fasten off, pull magic circle closed and weave in ends.
Make two hearts for either the bag or pillow.