It does seem like a big shift in her attitude towards you. Other emails she sent were almost accusatory for no reason.

I think you should reply in a business casual style but emphasize the positive stuff like " so glad the accountant seems to be working out"

Regarding the health insurance hike I would only ask her for information and make the financial decision with out her opinion on the matter.

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M 39
H 35
D5,D4
M 4
T 9
ILYBNILWY 5/18/11
Left 7/11/11
Divorced 12/1/13