I believe that Catrikes are supplied with clipless type pedals requiring the use of cleated shoes for foot retention. This works well, but it's not for everyone. I rode clipless pedals for years, but in the last few years foot pain issues forced me to abandon them in favor of platform type. On my trike, I initially tried heel straps attached to toe clip cages. These worked great, but they were difficult to get in an out of. Last week I switched to a set of Power Grip straps and like them very much. I have yet to take a long ride using them, but I think they will be exactly what I need.
I really don't think that studded MTB pedals will add much to prevent foot slips and recommend that you try a more positive foot retention system. If you are determined to try studded pedals, I'd recommend buying the cheapest set of aggressive stud pedals to test out. If your wife likes them, then you can invest in a better set.
Good luck and let use know how it goes.