Review the original item:
After the thunderstorm, Teresa splashed through the puddles left on the
street,
she enjoyed the cool rainwater on her hot feet.
You chose the correct way to fix the error:
After the thunderstorm, Teresa splashed through the puddles left on the
street,
for she enjoyed the cool rainwater on her hot feet.
Teresa splashed through the puddles left on the street is a main clause. She enjoyed 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.