She didn’t know whether to go to the party or to stay home.

The phrase "to go" is correct in this context because it maintains the parallel structure of the sentence. The construction requires two infinitive forms: "to go" and "to stay." In English, when presenting options like this, particularly with the conjunction "or," both parts should be in a similar grammatical form to ensure clarity and coherence in the sentence.

Using an infinitive ("to go") complements the structure of "to stay" nicely, providing a balanced and grammatically correct phrase that allows the reader or listener to understand the choice clearly. This format, using parallels with infinitives, is particularly important for maintaining the flow and readability of the sentence. Hence, "to go" fits perfectly within this grammatical framework, leading to the proper construction of the complete thought conveyed by the sentence.