I think a lot of times when people pass away family or friends that are not in the area often don't get the chance to have some momentos of their loved ones, especially if no family live close. But even when family are close they aren't able to get things to others or it isn't important to them so they don't bother. Perhaps her diagnosis was a reminder of some similar situation and she wanted you to at least have something of hers. Perhaps they are favorites of hers. I think thanking her for being so considerate, with an added "hope we have you for a long time yet" will seem less -should I say morbid.