My little sister is a big baby; she cries all the time. correct punctuation

Yes, if that's a semicolon after "baby" it's correct.

Mr. Smith, my Spanish teacher, is going on vacation

Well, it sounds like your little sister is a big "baby"; she cries all the time!

To correctly punctuate the sentence, you can make the following changes:

"My little sister is a big baby: she cries all the time."

To correct the punctuation in the given sentence, you would need to add a comma before the phrase "big baby" to separate it from the rest of the sentence. The corrected sentence would be:

"My little sister is a big baby; she cries all the time."

This use of a semicolon is appropriate here because it connects two independent clauses that are closely related in meaning. The semicolon shows a stronger relationship between the two ideas than a period would.