Ahhh i feel so awful!!! advice please?

yesterday i was at the beach for a friend's birthday party. her boy friend had gotten her this beautiful sterling silver necklace. we were about to go swimming so she asked me to take it off. so we're standing out in the waves like a bunch of idiots and im trying to be super careful but we got knocked over and the little heart pendant slipped off and got swept away. i felt so awful. they were both completely understanding that it was an accident but were both crushed at the same time. we looked for it but couldnt find it. i apologized profusely. i promised to by her one just like it, but she said it wouldnt be the same. also i wont have that kind of money for a very long time. what do i do?????? i feel sooooo bad.