Ridge vents actually prevent rain and snow from entering the house. They work in conjunction with soffit vents to keep the roof cool. My first thoughts are unless you're getting a truely horizontal rain or a rain that comes from the ground up, then the vent may not be installed properly. One common item that's overlooked in the installation is the silicone-caulking of the nails/screws that are used to hold the vent in place. Buy some 100% clear, silicone caulk. Caulk the nails/screws holding the vent in place as well as any OTHER nails/screws along the roof line. (Walk end-to-end to see.) You can caulk where the 'foot' of the vent meets the shingle too if you wish because if the opening in the ridge was made TOOOOO big for the vent, wind may blow rain up underneath the 'foot' of the vent, and into the house.
You may want to do an inspection from the inside too looking for rusty nails/screws on the underside of the roof, especially where the vent is. Also, inspect the ENTIRE under-roof because water WILL travel from the strangest of places. Look for dried spots too. Of course, during the next heavy rain (after you caulk), go up there to see if you can actually see water coming in, and follow the trail. Make sure you caulk in the right weather. If it's too cold, it won't take. AND, do it from the ROOF; not underneath.
WHen you're finished, replace the damaged insulation and fix the ceiling in the bedroom. (Until the water is stopped, this fixing may need to be re-done.) My best to ya and hope this helps.
PS: Is the ridge vent too short? Check the ends, but if you caulk the 'foot' of the vent all the way around, you should be OK.