Answer:
She reached late; luckily, the bus had not left.
Step-by-step explanation:
A semicolon is generally used to connect two independent clauses that are closely related. And in the use of the semicolon, the word acting as the conjunction between the two independent clauses must be followed by a comma.
So, the given sentence "She reached late luckily the bus had not left" can be correctly rewritten as "She reached late; luckily, the bus had not left".