I vote for option #1, but maybe just because my T is forgetful. So maybe #1 or #2 for your T. If #2, it would have been good for her to start with, "I know you didn't want to discuss this letter, but it's so important, can we spend a little time on it?" That way she acknowledges your wishes, you don't feel ignored, and you have a last chance to veto the idea. Option #3 sounds too vindictive and like game playing, so I don't think that was it.

When she started reading the letter, you didn't ask her not to? Could you interrupt and say, "oh, you must have forgotten but I don't want to go over that letter in session." That helps her and her poor memory out.