Answer:
B) she
Step-by-step explanation:
The first comma after the word "dinner" is necessary because "After dinner" is an introductory phrase. So, we must put an introductory comma there.
The comma after "dishes" is necessary because the word right after is "so", which is one of the coordinating conjunctions (FANBOYS: For, And, Nor, But, Or, Yet, and So). A comma always comes right before one of these conjunctions.
The final comma after "cake" is also necessary because the sentence is listing out three or more items: great meal, birthday cake, and gifts. This is called a linker comma and it always separates items in a list.
Thus, the comma that is unnecessary is the one after "she" because this provides an unneeded pause in the middle of the sentence.
Hope this helps!