I wouldn't want to take over from the grandma who is teaching the girl to sew. That's quality time for them to spend together. Instead I'd suggest that the girl finish up the projects she's started (she probably hasn't and that's why she's looking for another teacher) and then ask for something more interesting to her. Explain to her that everyone needs to start with the basics, and that's what the grandma is teaching her. Then she can quickly move on to other projects.