The researchers said that about 550 Western women were living in the Isis-controlled area of Syria and Iraq, where their main responsibility was to be a good wife and mother.
Some women had expressed a desire to fight on the front lines, but it was not allowed under the Islamic State's interpretation of Sharia law.
But Western women were playing a significant role in propaganda and the recruitment of other women.
"Isis has allowed for, and even relied upon, a decentralised network of messengers to carry and promote its propaganda and proliferate its world vision," the report said.
The report highlighted the case of Salma and Zahra Halane - the teenage "terror twins" from Britain - who encourage women to migrate to Isis-held territory.
They also answer questions from would-be migrants. Salma advised a woman on Ask.fm that she should marry as soon as possible after she arrived.
Smith said the longest known period of a woman living unmarried in the Islamic State was two months.
Women also know their marriages might not last long, the report says, citing "Shams", a Malaysian doctor who is prolific on social media and whose husband proposed on the first day they met.
She posted a picture of her wedding, for which she wore a white niqab, and wrote a caption on the picture: "Marriage in the land of Jihad: 'Till Martyrdom Do Us Part'."
Using social media platforms such as Twitter, Facebook, Tumblr and Ask.fm, the researchers monitor about 100 women from 15 countries who they believe are living in Isis-controlled territory. The majority are in their late teens and early 20s; the youngest is 13.
And though the researchers said marriage wasn't the only reason women were joining Isis, it was still a factor.
"Online, images of a lion and lioness are shared frequently to symbolise this union. This is symbolic of finding a brave and strong husband, but also propagandises the notion that supporting a jihadist husband and taking on the Isis ideology is an empowering role for females."
The report also highlighted discrepancies between the utopian society presented through Isis propaganda and the reality.
Women have been increasingly raising concerns, albeit indirectly, about issues including inadequate healthcare, shortages of electricity and clean water.
One woman reported having a miscarriage in the hospital after she was unable to communicate in a common language with her doctor.
The researchers also suggested ways to counter the recruitment of women to Isis. They said highlighting what life is really like in the Islamic State - puncturing holes in the utopian propaganda - would help to deter young women from going.
They also recommended boosting the number of female mentors and caseworkers working with vulnerable young women, saying there was a lack of persuasive female voices reaching these women.
Behind the lines
550
Western women were living in the Isis-controlled area of Syria and Iraq
13
Believed to be the age of the youngest. Most are in their late teens and early 20s
2
Months, longest known period of a woman living unmarried in the Isis-controlled area
