Regarding a towell, you will need one for sure. However, be careful on the type you bring. For me, I wouldn't want to carry the usual cotton towel we enjoy from home.
For years, I would use the microfiber backpacking type of towel. These are extremely lightweight, dry quickly, clean easily, pack small. A quick search of "backpacking towel" will bring several options and sizes. They really do work great.
For the past several years of travel, I have been carrying a sarong and don't like to go anywhere without it. It is perfect for me because it does the same as the backpacking towel plus MUCH more. Even for a guy like me, a sarong works wonders. With that in mind, I only travel during warmer months, so I don't need a towel for warmth necessarily. Might be the only downfall of the sarong.
The point being, a cotton towel can take up too much space in your pack, be heavier, and take forever to dry in cooler months. Pew!
May you and your wife have the best of all journeys.