Well, at least you finding it, has stopped her worrying and wondering. If it said a reward for information - you provided her with more than enough information....
The reward will probably be covered by her pet insurance, but I don't think I could bring myself to ask for it. Does she have your details to come back to you?
if it was a mobile phone number you contacted her on, send her a text asking if she is ok and saying how sorry you were to be the bearer of bad news, add your name and a sad face thingy and then she has your mobile number and name and you can see if she gets in touch