Here is the original item:
Circling the parking lot,
(A) Dominique
searched for an empty space close to the mall
entrance (B)
so that an afternoon thunderstorm would not drench
her (C)
while she was loaded down with good buys.
You wanted to do this:
Circling the parking lot, Dominique searched
for an empty space close to the mall entrance. So
that an afternoon thunderstorm would not drench her while she was loaded
down with good buys.
Adding a period after entrance makes a fragment. So that an afternoon thunderstorm would not drench her ... is a subordinate clause. This type of clause cannot stand alone as a complete sentence.
You might want to review the rules.