How did they establish that she consented? This article doesn’t say, but it was probably from the testimony of the men involved. Traditional Islamic law disallows a woman’s testimony in such a case. From the BBC, with thanks to Kemaste:
A teenage girl and two young men in Iran have been sentenced to lashes for having sex.
The court dismissed the girl’s claim that [she] was raped. It said she had sex of her own free will, the official Iran Daily newspaper reported.
The girl was sentenced to 100 lashes because her accusations of rape and kidnap could have landed her partners a death penalty, the Tehran judge said….
The young men in the case were sentenced to 30 and 40 lashes each. …
Under Iranian law, girls over the age of nine and boys over 16 face the death penalty for crimes such as rape and murder, while capital punishment can be imposed in certain cases of illegal sexual relationships.
Nine year old girls facing the death penalty for rape: do you think they are the perpetrators?