Todd:
Welcome!
The WR250/450 are good bikes, you won't go wrong there. For the most part, howvere, you can pick you favorite color, they are all good bikes.
In any brand of bike you will find the low end "trail bike", the high end MX bikes and then the bikes that try to find a middle ground. The Wr series is such a bike. They have the high performance motors, full travel suspension, lightweight frames. They also have a few features, such as a kickstand, headlight and electric start. I have a WR450 that I really enjoy.
There isn't much of a weight difference between the 250 vs the 450 so I would recommend the 450, just because. Unless you are serious racing you won't need that extra power 95% of the time, but when you do it is nice to have.
Since you are not very tall you might want to consider some lowering options. Many bikes, the WR included, have "lowering links" available that will allow you to lower the rear suspension without losing all your spring pre-load. You can slide the forks up a little higher in the clamp (may need to raise the handlebars up to provide room) and shave the seat down a bit. You shoud be able to get the seat height down a good two inches.
My daughter is only 5' 2" and I ended up buying her a Honda CRF250x because it has the best lowering options. Before I lowered it I took it out and gave it a good trail ride, and it seemed to perform every bit as well as my 450.
My daughter and I both race enduros, and the bikes are serving us well.
Rod