To her credit, our American Muslim friend doesn't deny that Muhammad had sex with Aisha when she was only nine years old, as this would contradict numerous ahadith reporting Aisha's age:
Sahih al-Bukhari 3896—Narrated Hisham’s father: Khadija died three years before the Prophet departed to Al-Madina. He stayed there for two years or so and then he wrote the marriage (wedding) contract with Aishah when she was a girl of six years of age, and he consummated that marriage when she was nine years old.
Sahih al-Bukhari 5158—Narrated Urwa: The Prophet wrote the (marriage contract) with Aisha while she was six years old and consummated his marriage with her while she was nine years old and she remained with him for nine years (i.e. till his death).
Sahih Muslim 3310—Aisha reported: Allah’s Apostle married me when I was six years old, and I was admitted to his house when I was nine years old.
Sahih Muslim 3311—Aisha reported that Allah’s Apostle married her when she was seven years old, and she was taken to his house as a bride when she was nine, and her dolls were with her; and when he (the Holy Prophet) died she was eighteen years old.
Sunan Abu Dawud 2116—Aishah said: The Apostle of Allah married me when I was seven years old. (The narrator Sulaiman said: Or six years.) He had intercourse with me when I was nine years old.
Nevertheless, it's always disturbing to find a Muslim woman defending such a horrifying practice. According to the Hadith, Aisha hadn't even reached puberty when Muhammad had sex with her:
Sahih al-Bukhari 6130—Narrated Aishah: I used to play with the dolls in the presence of the Prophet, and my girl friends also used to play with me. When Allah’s Messenger used to enter (my dwelling place), they used to hide themselves, but the Prophet would call them to join and play with me. (The playing with the dolls and similar images is forbidden, but it was allowed for Aishah at that time, as she was a little girl, not yet reached the age of puberty.)
While our American Muslim friend attributes Muhammad's sexual relationship with Aisha to the culture of his time, this simply won't do. Muhammad is different from everyone else in Arabia, in that Allah declares him to be the pattern of conduct for Muslims (Qur'an 33:21). In other words, by having sex with a prepubescent girl, and by delivering a revelation declaring himself to be the ideal pattern of conduct for Muslims, Muhammad actively promoted sexual intercourse with prepubescent girls for all future generations of Muslims (unless, of course, you believe that Western values trump Allah's words in the Qur'an!).
Since our American Muslim friend defends Muhammad's actions, she is defending one of the most shocking, sickening practices known to man. Behold the impact of Islam on the mind of the American Muslim.