You can bring your fiance from Peru and marry her in the US within 90 days of her entry. However, if you want to go back to Peru to live with her there, she will be unable to get a green card until you apply for her. Therefore, if you are a US citizen and want to return to the US and bring her with you, you will then have to apply for a green card for her at that time. If you want her to get a green card immediately, you will both have to live in the US during the period of time that you are waiting for her interview and then for 2 years after she receives her green card, to get a permanent green card. You can obtain an advance parol for her to go back to Peru for a visit, but not to live there.