We wnt to Disney with freinds a few years back, both wives were about 22 weeks. They did have an issue with no seeing scary things while preganat so we had to avoid Haunted House etc. I think this was a person or cultural belief.
We had no other issues except not to set too high and expection on amount of walking etc.
As long as she doesn't go on any rides that have warning signs not to ride them if you're pregnant, I don't see a problem. She's pregnant, not infirm
We went on vacation to London and Paris when I was 22 weeks pregnant with our second son. The only person who had trouble keeping up to the brisk walking pace was my oldest son LOL I know some women have trouble walking, etc. during pregnancy, but if your wife is not having problems with the regular stresses and exercise (walking, etc.) involved in everyday life, I'm sure she'll be just fine!
Have a great time and congratulations on your upcoming bundle of joy!