Generally speaking, quilt classes do not last like a retreat does so it is not quite the same dynamic. I would not let one person keep me from going to a class or even a retreat as I would not give anyone that kind of power over me.
Whatever the minor issue or issues that caused the initial rift were, they are in the past. Unless the same issues will come up again, I would leave it in the past and not bring it up unless the angered woman chooses to address the issue. Even then I would try not to be reactive. Without more data to go on, a blind stab in the dark here is that there is a real issue bothering this woman that is not any of the stated ones she gave. Others saying to be understanding also supports there is something else affecting this woman's whole life.
If you find she is affecting your enjoyment of a class, you have more options than just not going to classes. You can find the same kind of class at another time or even another venue.(my quilt shop has more than one session of any given class to accommodate different schedules.)
You can confront the woman and tell her you want to enjoy the class so would like to leave her issues at the door. The real key is not to lose your temper with what you are seeing as childish behavior. You can talk to the class organizers to see if another time / class can be arranged so you can choose to avoid unpleasantness. It sounds like your friend who did not get an apology is your real issue as you want to show support and the problem is with her and your friend more than with you.(guessing here) Your friend who has not gotten an apology, would she accept one if it was offered? Can you be supportive of your friend without any intercession with the angry participant?
Whatever you choose to try or do, keep in mind that if you can shift your own perspective you can find a way to deal with this woman. If you can shift hers, you are doing a service that may or may not be respected or valued. Probably easier to shift yours and your friends, and your friend may not see the wisdom in such a shift.
The bottom line is that you cannot change anyone but yourself. I hope you do not lose the group over one participant. There are other groups, or can be.