Assisted suicide?
OK, I admit that some strange ideas pop into my head from time-to-time, but I couldn't help thinking that Armande's death was actually a suicide assisted by Vianne. It's revealed that Armande is diabetic. Vianne knows this. Armande is also deathly afraid of the "retirement home". Vianne knows this, too. Armande could have been getting to the age where she would no longer have been able to keep herself out of the hated retirment home (involutary commitment).
The birthday party had chocolate on just about everything. Vianne knew about Armande's diabetes, but threw a big chocolate feast for her anyway. Armande dies shortly after the party. So the birthday party could also have been a "send-off party" as well. Suicide by chocolate overload?
I know it sounds crazy, but this idea came to mind immediately after I realized Armande was dead... I can't stop thinking about it. What do you think?