The Genevan government burned Michael Servetus at the stake, after Calvin accused him of heresy (he denied the Trinity). Contrary to the stereotype, Calvin did not run Geneva, but he was the religious leader and had huge influence (roughly equivalent to the role of the Pope or an archbishop in a traditional Catholic country–i.e., there was a church-state distinction, but the Church was extremely powerful).
The whole fracas allegedly started while Servetus was living at Lyons in Catholic France practicing medicine. A young man from Lyons had become a Protestant and was studying at Geneva. His mother was writing anguished letters to him begging him to renounce his “heresy.” To which the young man responded that Catholics at Lyons were in no position to criticize the Protestants as heretics, because one of the most notorious heretics in the world was living at Lyons. The Catholic lady made inquiries and discovered that this was so, and Servetus was denounced to the Inquisition. (This at least is the account I’ve read in a secondary source–I haven’t read these letters myself and don’t know for sure that this was the cause.) As a result, Servetus was condemned to be burned at the stake and had to flee France. For some strange reason, he chose to pass through Geneva, and actually went to hear Calvin preach. This was really stupid because Calvin had been denouncing Servetus as a heretic for years. He had said in a letter to a friend (though Servetus probably didn’t know this), “I hope he never comes to Geneva, because if he does it will be my duty not to let him leave alive.” Sure enough, Calvin accused Servetus of heresy before the Genevan government (which according to Genevan law meant that Calvin had to go to jail until the trial), and Servetus was condemned. Calvin wanted him beheaded, but the civil government chose to go with tradition and had him burned alive. Most church and state leaders (Catholic or Protestant) approved of this at the time.
Some other people were executed for “blasphemy,” but I believe there were political issues at stake there (they had tried to overthrow the government as well as the religious regime). Another guy named Jerome Bolsec was imprisoned for attacking Calvin’s doctrine of predestination. There’s some speculation that Calvin may have wanted to have him executed, but in this case the other Reformed leaders in the area protested that this was a relatively minor, speculative issue and Bolsec was released.
Unlike the Swiss Reformed city of Zurich, Calvin’s Geneva did not (as far as I know) drown Anabaptists. Calvin attacked the Anabaptists in print but dealt relatively gently with them in practice.
Essentially Calvin’s attitude to religious freedom did not differ much from that of the Catholic Church.
If your friend wants to become Mormon because she’s fed up with the violent past of orthodox Christianity, she should look into Mormon history a little more closely. If I’m not mistaken, early Mormons in Utah had people executed for religious reasons, and I’m pretty sure that they had death squads that killed people perceived to be enemies of the church. Mormonism is not the place to go if you want to get away from a history of religious violence. Has she looked into the Mennonites?
Edwin