Simon,
Your email to her (which I reread) has a "mixed message." On one hand, it is very warm especially where you told the florist to go wild. On the other hand, you referred to an idea that she might throw away the flowers, even though she said nothing of the kind in her thanks to you. You are correct that she's capable of this. But it's somewhat "provocative" to mention it after she has apparently thanked you sincerely. Possibly she was trying to "repair" the damage of her email by being nice about the flowers you sent. And your comment didn't allow her to make the repair, so she counterattacked viciously, wreaking more damage. I'm not saying she didn't deserve your comment, but making such a remark may perpetuate this dynamic of insecurity, anger, and inability to repair damage. Does this make any sense..?
bunny