Prison rape is all too often a common occurrence. It's strange but a hetrosexual male won't have sex with another man outside the walls but will often have sex with a male behind bars.
Being in protective custody is no answer either as rape happens even in protective custody. Those inmates are protected from the balance of the general population but not each other and are considered among the lowest ranking inmates by the rest of the prison population..
If this individual proceeds with criminal charges against the other inmate, if they thought life was hell in prison before, try it after you "rat" on someone. You're fair game for everyone after that as being a "rat" places you among the lowest of the low. Generally only the child molesters rank the lowest among the inmate pecking order but a "rat" is right down there even if they have a just cause
The safest place I think would be in administrative segregation for this individual. and if it it's denied, then a legal lawsuit against the department of corrections is in order.
Hopefully nothing like this ever happens to this individual again.