I am undecided/not convinced that AG and/or her husband has anything to do with NG's disappearance. If they do, I hope they are prosecuted to the fullest extent. If they don't, I can't imagine the pain that they and the rest of the family is and will go through for the rest of their lives.
I am the local daughter that has the responsibility of caring for my mom who has some dementia. It can be both a blessing and a curse and can be a source of some very difficult family dynamics - even in the best of families. I can imagine that there may be a certain amount of resentment from AG towards SG & CG - not that she doesn't love them and can even be proud of/happy for them and their success. But it can be very hard to be the one that is faced with the day-to-day care of an aging parent. Even if NG wasn't in need of full-time "care", there is still the sense that you (AG in this case) are the one to make sure she is OK, that she gets to appointments, social things, has/takes her medicine, runs errands, makes sure household and financial things are done, etc. And you do this day in, day out while your siblings live far away and may seem blissfully unaware of the day-to-day care you provide. It often feels like you are the sole person responsible for your mom's health, safety, etc.
So when this tragedy happened, even if AG had nothing to do with it, I can easily see how she could feel responsible/guilty and/or even feel like the rest of the family is blaming her. Add to this that this is a very public case and there is so much speculation that AG and/or her husband are involved and that many in the media/social media are openly saying they are guilty. Imagine how difficult it must be to deal with your mom being missing under this circumstances and then having to cope with the public blame and worry if your own siblings may believe you are responsible. And even if they aren't "responsible" in the sense that they harmed NG, the pain of feeling responsible because you were the last one to see her and that you didn't keep her safe and wondering if your own siblings are questioning your involvement must be unbearable.
One of the things I love about Websleuths is that it is victim-friendly so I am kind of surprised that there has been so much posted here openly accusing AG and/or TC of being involved. I understand and respect that Websleuths is where we share our thoughts, theories, etc but I always thought that we weren't supposed to speculate about someone's involvement unless/until they were named a person of interest by LE. I really hope that AG (and TC) had nothing to do with this and that somehow the family will be able to heal at some point.