okay, I've read through all the comments so some of what I'm going to say is a duplication but not all.
I quilt and I sew, both with serger and regular machine.
1. stabilize the Minky if you have a light weight interfacing.
2. Whether or not you can stabilize, have Minky on the bottom, near feed dogs when you sew.
3. put an almost continuous line of pins parallel to the seamline just outside the area that will be trimmed with the knife. do not remove them before sewing.
4. Sashing does not have to be the same fabric line as the main quilt, in most case it isn't. Pick a color that picks up one in the quilt pieces or a complementary color (opposite side of the color wheel).
5. Since she is already a big girl,be sure that you are making this big enough for a nap on the couch etc.