I'd been wondering how you were going Tiggermad.
You don't have to 'do' anything. Of course you can accept her apology if you wish but you don't have to make up (whatever that involves).
Please remember: apologies are easy for people to make because they are only words. Quite often, apologies are used to get another person back into line. If they don't lead to changed behaviour they are actually pretty worthless in the great scheme of things. You can simply say Thank You. That is an example of tit for tat. She says sorry - you say thanks. Don't give any more than you're getting. Don't agonise over it. You don't have to 'make up.' Her reaction to you not over compensating and throwing herself at your feet with gratitude will tell you all you need to know.
Also, the cycle will start again only if you attend the 'party' that she's inviting you to. So have a good think about what you're prepared to do. If you have your strategies and scripts written down somewhere - in your Notes on your phone say - then you can refer to them as necessary. And stick to them. She will throw every trick in the book at you to get you back 'under control.' But you can hold your ground.
I also don't necessarily think as another PP has suggested that you now need to jump in and outline all the errors of her ways. While it is very tempting, that way often lies danger. It uses up a lot of your emotional energy, gives her ammunition to challenge, argue with and and use against you and then she gets to play the victim. Likely she will also recruit your sister or her friends as flying monkeys. I've seen this process play out many times. It's just not worth it. She doesn't want to hear it. You may as well shout into the wind.
Blocking her for periods, as you have done, is very sensible for your mental health. You have a lot of power in this situation. Don't assume you're at a complete loss here. You're an adult now. Ask yourself: what is the worst she could do: tell her friends or your sister that you're a terrible daughter? They're going to think whatever they're going to think. You don't have to react to anything they throw at you.
Guilt is operating here for you very strongly. It's expected that you will feel that guilt - because trust me, you've been strongly trained to by your mother and her allies - but you can also just sit with this discomfort and say to yourself 'that's my childhood training kicking in' and then you can decide to simply not act upon it. You certainly don't have to 'make up' because she's made you feel guilty for not complying with her dictates. Feelings of guilt are 'normal' in dysfunctional families but it doesn't mean they're actually normal in the true sense of the word.
Try not to let her behaviours, no matter how conciliatory they seem on the surface, change your plans going forward. You've actually got this. You have power. She can't ground you anymore.
You DO know what to do - it's just very uncomfortable. That means it's probably right. Remember to stick to your values of having a peaceful life and that will guide you.
Don't be surprised if you holding your line now brings extreme extinction burst behaviours from her: in my own family I've experienced tears, rage from enablers, accusations from relatives and hospitalisations of mother due to 'illness' I have allegedly caused by not falling into line with the matriarchal cult. It can get pretty intense so look after yourself and please keep posting.