Take a look at the original sentence again:
After the thunderstorm, Teresa splashed through the puddles left on the
street, she enjoyed feeling the cool rainwater
on her hot feet.
You chose to fix it the correct way:
After the thunderstorm, Teresa splashed through the puddles left on the
street, for she enjoyed feeling the cool
rainwater on her hot feet.
Teresa splashed through the puddles left on the street is a main clause. She enjoyed feeling the cool rainwater on her hot feet is the second main clause. A good way to fix a comma splice is to use a comma and a coordinating conjunction like for.