Final answer:
The word 'however' in the given sentence functions as a coordinating conjunction, joining two independent clauses and introducing a contrast.
Step-by-step explanation:
In the sentence 'Our new assistant is very efficient, however, she is often late getting to the office,' the word however functions as a conjunction. Specifically, it is a coordinating conjunction used to introduce a contrast to the statement that comes before it.
Coordinating conjunctions connect words, phrases, or independent clauses that are grammatically equal. The conjunction here indicates that while the assistant is efficient (a positive trait), there is a contrasting attribute (a negative one) which is her tardiness.
As a tip, similar to the coordinating conjunction 'but', 'however' needs a comma before it when used to join two independent clauses, as it is directly connecting these clauses to show contrast.