You said she and her husband share a email address. It is possible that there is something not right in their relationship. Have you thought whether there could be some domestic upset happening. It seems very weird for a 20 year+ friendship to end without explanation. Are you in contact with any other joint friends or relatives. Maybe you could contact one of them to voice your concern (don't mention possibility of domestic upset unless anyone else has similar concerns). It could well be that the husband is controlling the situation. Tread very carefully!
Anger management!!! Help needed.