As you can see, this girl made quite a mess of this lining. The tear was near the seamline, but not actually a rip in the seam. Stitching that area closed would only make the lining width smaller and the next wearing would have the same results...another rip.
|The first thing to do is find lining that matches. After that, I cut a large triangular piece of lining that would fit in the space left by me spreading the ripped area apart a bit, forming a triangle. Then I sewed one side of the triangle from hem to point. After that I sewed the other edge from the point to the hem.|
|The right side of the skirt lining looks like this. It's a little tricky to get the apex (point) of the triangle to lie flat and not bulky. Just remember to trim the seam allowance after you get the right side looking good. If your gusset is on the outer fabric of a garment, where it will show, you may need to rip and redo a few times to get it right. Here, though, it hardly shows since it's on the inside.|
The bottom edge looks like this. As you can see, I've left plenty of extra fabric. When you are manipulating that triangle to get it in the perfect position, you don't want to worry about running out of hem allowance. Just finish it off to match your garment and you are finished...lots more room to move!