You and your wife have handed it well so far . Leave it alone for the moment , let her husband and family try to help her admitte to her problem . Sometimes bad things happen to people that cause these problems . I have seen it so many times it is not funny . hear are some examples
Pregnant women can be fine but after child birth they may get hormonaly affected ,it can also happen when they stop breast feeding .I am NOT talking about about post natal depression ,but a true Hormone change .
They suddenly ,or over time, start to remember something they have bured away in their memory such as being molested as a child ( very common) . This can happen out blue when say a relative who had molested them and they have not seen for decades moves back into town etc.This starts to dominate and override their personalty and starts to eat away at them,it is a bit like a dull pain that never goes away .
Medical conditions like early one set of some cancers or brain tumours
Finacial problems such as a gabling habbit that is just starting to be discovered.
You and your wife are a victim of her symptons ,you can not solve her problems ,nor do you even know what they are . Just be a friend to her and her husband , do not allow her to be tempted LOCK the medician and valuables away . If her husband admitted he has noticed it over the last month he has probably had a funny felling for a while . Help him when he needs it ,encorage him and his his wife to enjoy themselves like small trips away . Sometimes people can get better if things change around them and they are happier ,but sometimes medical help is needed.
If you go to church talk to your minister without naming her and ask him for advice .
Just remember what would you like to happen if it was your wife .