1) I don't think it have to be a specific reason, theory or something like that. May be Nikki just feel comfortable with the dolphins and as he was excited to swim with them the ability to speak reach his mouth.
2) I think, as everything nowaday, is just a media exaggeration. Not everything has an explanation, somethings just happends by destiny.
3) I heard that dogs can decrease the pain in people with illnesses like cancer.
4) May be she had a really god job or she sold her house in order to be able to pay the trip.