The Glovner, you need to read the immigration rules. Here's the relevant bit:
284. The requirements for an extension of stay as the spouse or civil partner of a person present and settled in the United Kingdom are that:
(i) the applicant has limited leave to enter or remain in the United Kingdom which was given in accordance with any of the provisions of these Rules, other than where as a result of that leave he would not have been in the United Kingdom beyond 6 months from the date on which he was admitted to the United Kingdom on this occasion in accordance with these Rules, unless the leave in question is limited leave to enter as a fiance or proposed civil partner or unless the leave in question was granted to the applicant as the spouse, civil partner, unmarried or same-sex partner of a Tier 1 Migrant and that spouse or partner is the same person in relation to whom the applicant is applying for an extension of stay under this rule; and
Your fiancee did not have permission to remain in the united kingdom for more than 6 months when she entered the country, and she doesn't qualify for any of the exceptions- she wasn't on a fiance visa, and she didn't enter as the spouse of a Tier 1 migrant. Therefore, she cannot meet this portion of the rules.