Is this childish or am I just being plain unreasonable?

[LordsOfTheFlies]

My sister and I have never been particularly close ... I'm not sure why, I guess it's just the way things are.

We generally only do birthday cards in the family, and I know that my sister has for the last few years has sent out birthday cards late, and she had completely forgot our nieces 21st birthday (birthday was in April and gave her a birthday present at Christmas - they live a 15 minute drive from each other)

Anyway things have been quite hectic lately with personal things going on in our life. My niece had a birthday in February and because we rarely see each other it completely slipped my mind and I didn't send her a birthday card.

Today I get an email from my sister asking what was wrong and why didn't I send a card to DN?

... Now it wasn't done intentionally at all, but my sister does this all the time, send cards weeks after it was someones birthday and no-one says anything because it's not a big deal.

Aibu to think she should have just forgot about it and not let it bother her when she has done exactly the same?

Message back saying thanks soooo much for checking but you really are fine and it is very kind of her to show such concern. Say sorry about the card but you knew she'd be OK if you hand it over next time you see them.

Very PA I know

SIL is being childish.
I like what Goldmandra said.

Tell her you were surprised she was anxious about the missed card but was under the impression she didn't give a fig about cards being received on time seeing as she doesn't give the same consideration to everyone else.

She is being unreasonable.

Well it's an email so you can't "read" tone of voice.
But is it not possible that your sister is actually genuinely concerned about you - because it is so out of character for you to forget your niece's birthday (by some weeks now if her birthday was February)? Rather than a dig about it?

Pick up the phone perhaps?

Definitely say, oh gosh yes sorry we forgot, but I didn't realise you'd mind getting one late since you always send yours out late too?

You can't let this one pass by! It can't be one rule for her and another for everyone else.