There are a fair number of slow rides that pregnant moms can ride. There are also lots of shows to see, parades, fireworks.
Also, pregnant moms often don't have the stamina (or food tolerances) they normally would have. A targeted approach is wise. more time in the pool is also wise.
They also don't have the normal emotional tolerances either. You might find yourself crying at the sight of Mickey - or angry when you don't get your way. Try to keep in mind your elevated hromone levels!
Just as small kids manage to have fun, so too can pregnant moms. One ride that should be avoided - which doesn't seem like an obvious problem - is the safari ride. The bumps seem like nothign when you aren't pregnant - are not good while pregnant.
Instead of focusing on rides, and what she CAN'T do, a pregnant mom can spend a little time kid watching - knowing that's she's going to have her own soon. Maybe she can spend a little time talking to other moms, getting ideas for names.
This may sound odd, but it might also help to use a trip to WDW as a pregnant mom to take a look at some of the other families. For example, most of us don't see kids with disabilities in our daily lives all that often. While you wouldn't want to be rude, having an opportunity to see these amazing kids at WDW, and their amazing parents can be a real eye opener. Likewise, seeing say grandparents managing to keep up withteh grandkids can be a revelation. Seeing parents dealing with a meltdown - even if they are handling it poorly - can also be instructional for a mom-to-be. Try approaching this special visit with a little 'outside-the-normal-box' mentality.
One more no-no: hot tubs! Dipping your feet in is probably fine, and the pool can be GREAT - but deep dipping in the hot tub is not a good idea, as it can raise your body temps to dangerous levels for baby.
One last fun idea- try getting a message at one of the spas! It can be fun.
Mind, this is all assuming a normal pregnancy.