I believe you. You did nothing wrong. You were taking pictures at a place, where people take pictures.
I can totally identify with your reaction. So many times when something has happened, when something has gone wrong and I am involved, I revert to that little kid, who felt so guilty and responsible..who perhaps by feeling he was responsible, he also felt some control of a world that felt overwhelming. I start to get anxious and all those feelings of guilt and shame emerge..and make it difficult for me to stand still and respond. I "catastrophize".
I wish in those moments, and in yours, we could stop the action, perhaps call a friend for a different perspective and then step back in and at least know we have support..we can't do much about that family but we also don't have to take on their anxiety.
Yes, there are sick people, but that does not give anyone the right to be mean or hurtful. Her sickness may be fear.
I am so glad you did something beyond isolating (which is often my reaction). By coming on here and telling people, you took a step in change, you trusted us with your feelings and fears, and in turn I hope you got not only affirmation for you on that day and in that moment, but for you as person.
Btw, I love your signature about how you got your name.