We never co-slept but consistency has been key for everything with us. You just need to be firm and consistent.
IMO, Instead of jumping to solely CIO do a gradual CIO. Leave her for 5m, then go in and console. Repeat at 10m (start the time over, 10m from the time you left the room), then 15m, 20m, etc. and you shouldn't need to go past 60m. If you do, I'd just try again the next night.
Eventually the CIO should shorten every night.