Changing rsvp Due to Covid

I would say if you know for sure that you will not be attending, I would let her know asap. That's better than not telling her at all and having her pay for a meal for a no-show or waiting until last minute that she can't change her guest count.

I don't think you're wrong for changing your mind. Say you're sorry it's so late, but with how things are you just don't feel comfortable going. She might be annoyed because of food counts and such but she is probably expecting at least some people will back out.

I would send a gift and a nice card though!

You shouldn't feel bad! These are extremely uncertain times, and anyone hosting an event should reasonably expect some people to back out. Sure, in a perfect world, you would have somehow known way ahead of time with 100% certainty what your RSVP would be, but in a perfect world, there would be no covid.....so please don't feel bad about changing your RSVP. It's way better to let them know than to be a no-show!

Health and safety is always more important than etiquette. But I agree you should tell her immediately; waiting will only make you feel worse and doesn't help her any. And know that she may be annoyed but that doesn't mean you have done anything wrong. Like PP said, anyone throwing a large event these days should be prepared for guests not to show.