Okay.
You may recall that at the end of S3, Seth and Kelly were going on a holiday to Africa.
In 4x01, Seth told Rudy that while in Uganda (iirc), they saw a small boy step on a landmine. If he moved, he and everyone around him would be blown up.
Kelly being a Rocket Scientist was able to figure out how to disarm the landmine, thus saving the boy.
After that, she decided to stay in Africa to use her power for good by disarming and destroying landmines.
Isn't that nice? I always knew she had a big heart.
