She wanted to visit Paris and London but she didn't have enough time.
Correct: A
Option A correctly places a comma before the coordinating conjunction 'but' when it joins two independent clauses ('She wanted to visit Paris and London' and 'she didn't have enough time'). Option B incorrectly places a comma between 'Paris' and 'and London'. Option C incorrectly places a comma after 'but'. Option D incorrectly uses a semicolon before 'but'; a comma is the standard punctuation for joining independent clauses with a coordinating conjunction.