Can I reinstall stock ROM without unlocking bootloader or rooting?

Hi guys,

Please help...my gf got some nasty virus on her mobile and I want to completely wipe the device a reinstall with stock ROM.
Can it be done easily without unlocking the bootloader? I guess factory reset wouldn't do the trick as the device is infected..
Can I flash the ROM using ODIN?
Please point me to the right direction.
Thanks
bulva