Thanks, everyone, for some good ideas. Dina, this is for the class that starts next Saturday.
I said that it has happened twice before. The first time, the lady told me she was going to come help. I politely told her I didn't need help and I never saw her in class again. The second time it was an elderly lady who had already taken the class who came to help her elderly arthritic sister to cut fabric (though I gave fabric cutting instructions before class). They were so far ahead of everyone else it caused problems. The current lady of concern is a friend of the two elderly ladies.
She lives about 15 minutes from here. My current thinking is to ask her to come with her friend for a short time to get her comfortable then to leave and pick her up at the end of the day. (It is a 6-hour class) Or, if she wants to stay and take the class she can have a discount for the referral.
I'm still pondering and welcome additional ideas.
Thanks everyone.