Dee Caffari sailed Aviva, an Open 60 sailboat, singlehandedly. She sailed a larger one singlehanded in her previous wrong-way round the world record setting voyage. Both those boats were heavily modified and upgraded to be single-handed by Dee. Most sailors aren't going to be capable of doing what she did, and it doesn't mean that your wife or you would be able to do it.
The main thing that decides how big a catamaran is big enough is how much crap you have to have with you. A person with spartan needs and modest means can cruise around the world in a 30' boat... if you need to have the large screen HDTV, the satellite phone, the stereo system, running hot and cold water, a big refrigerator, etc., maybe you should re-think what you're doing and stick to land.
Unless you're very wealthy.... a 48' catamaran is going to be a very expensive boat to own, operate and maintain. The costs on a boat go up geometrically, rather than linearly... a 48' boat does not cost 25% more to maintain/own/operate than a 37' boat.
One point on Chris White's book: yes, it is getting a bit long in tooth, and is in need of an update. However, if you look around, the average length of the cruising boat has steadily creeped upward. Tania Aebi's Varuna, which was a Contessa 26, was not all that unusual a boat to see out cruising back when she did her voyage in it.
The sailing press has slowly, but inexorably, pushed larger and larger boats as being necessary for cruising safely. Much of this probably has a lot more to do with the fact that most boat manufacturers are making larger and larger boats as a whole, since the profit margins on the larger boats is considerably greater than that on the smaller boats—the effort it takes to build a Pacific Seacraft Dana is not much less than it takes to build a Catalina 380... but one is easily sold for a lot more money than the other.
When cruising, I would highly recommend sizing the boat to what can be handled by the smallest crew person without the "powered" assistance of electric or hydraulic
winches—since that is what might be the case in a worst case scenario.
If you don't size the boat to this standard, and you end up in a situation where the smaller crew has to effect a MOB recovery or move the sailboat while the larger is incapacitated and can't... what do you think will happen?
As for the daughter being able to handle the 62' boat... is that with the electrical system failing, during a storm blowing 40+ knots, 30' seas, and trying to claw off a lee shore, with a dead engine, or is that in 75˚, sunny weather with light winds and calm seas. I'm pretty sure I know which it is... and if they needed her to do it in the other conditions, they might be in for a really rude awakening.
IMHO, you really have to look at cruising as a couple as two people single-handing the boat at different times, most of the time.