She's annoyed you forgot something she told you: what to do

Look at the length and punctuation of her message. A message that trails off or has no question mark often means she has already decided the miss is not worth dwelling on, and she is just letting you know she noticed. A message with a sharp question or a repeated word is more pointed and usually means it bothered her. Notice whether she used a name, a 'seriously', or an emoji. An emoji with a rolled eye reads as a light jab you can match. Flat text with no emoji reads as more hurt. The reading decides how much warmth to put in your reply. If she is light, a little self-deprecating humor works. If she is flat, skip the humor and be direct. Also check whether this is a one-off or a pattern. If she has mentioned you forgetting things before, the miss is carrying more weight than the single incident suggests, and the reply should say more than the usual one sentence of ownership.

The fastest way to end the annoyance is to bring the detail back yourself, with the specific piece you can now recall. Vague recall like 'the wedding thing, right' sounds like you are fishing. Concrete recall like the city and her role shows you took it in the first time and only lost the thread. That specificity does more work than any apology. Then ask one question that goes one layer deeper than the original fact, such as what she is most nervous about in the speech or whether the sister knows how much the planning has taken. A follow-up question is what turns a repair into a restart of the conversation. Keep the apology short. One clause, then the detail, then the question. If you can't recall the detail, say so plainly and ask her to tell you again. People generally respond well to honest forgetting more than to a guess that turns out wrong.

When she is annoyed, the reply should come within the same window she is active in. If she sent the message in the evening, answer within an hour or two rather than leaving it to sit until the next morning, because a long gap makes the miss look like it got bigger in your head. If you are going to be busy, send a short line now, something like acknowledging the miss and saying you will reply properly after your meeting. That buys you time without leaving her wondering. Avoid replying at very late hours with a long heartfelt message, since it reads as overcorrecting. Give it two or three days of normal conversation after a good repair. If she goes quiet after a sincere reply, send one light message about something new, not a second apology. If she still doesn't respond after a couple of days and nothing else in the conversation has changed, let it drop. Re-litigating a forgotten detail after she has moved on is the point where the miss becomes a reason to stop talking.