Ditto the advice about further training.
However, you don't need to feel at all guilty about letting the DM take care of your wife this time. It is possible that she got a little rattled by the loss of the fin, and though I'm sure she has confidence in your concern for her, she also knows that the DM is a pro and you are a newbie; therefore, the DM may have been in a better position to calm her down than you would have been. In addition, it's very tempting for people to let go--lose control of their emotions--when they are with a loved one, while on the other hand it's easier for them to get a grip when they are with someone in a leadership role.
Out of curiosity, did you discuss your wife's reactions with her? How did she feel about getting assistance from the DM? Was she disappointed that it wasn't you?