Dd is just two and for the 2nd time in 2 days we've had the same issue.
Both times she has done something and I'd like her to apologise. The first time she hit her baby (12w) brother and made him cry. I said something like, 'please don't hit Ds, its not nice. He's crying now, he's sad - you need to say sorry.'
The second time I stupidly left something out and she wrecked it. No big deal - I shouldn't have left it out. I caught her doing it, told her not to and asked her to say sorry again.
Both times I asked her to say sorry she had a massive, massive melt down and was sobbing like I was physically torturing her. The first time, stupidly, it became a fight about saying sorry:
Me: say sorry dd
Dd: (sobbing) no, no, no, I no sorry.
In the end I dropped it because I was worried thr it had obviously become a battle of wills about this bloody word and I thought I probably wasn't handling this the best way anyway.