My future in-laws belatedly sent me flowers for my birthday. I sent my future MIL an email thanking her the day I received them and dropped a handwritten thank you note in the mail. Yesterday, my fiance received a phone call from his mother, and I overheard her chastising him because I did not call her to say "thank you." He then put me on the phone, and she chastised me for not calling because she prefers the phone to email and just "likes to hear from people". It was too soon between my dropping the note in the mail and her call for her to have received my note.

Did I do something wrong? Should I have called her rather than emailed? The purpose of email vs. phone call is that she has been hounding us on the phone lately, and I didn't want to invite her to call me 5 times in a half hour as she has been doing recently. I am trying SO HARD and just can't seem to get anything right.