Re: SOMEONE HELP- RootCanal?!
I will give you a possible answer for your sister first. After you have a thorough cleaning from a dentist, plaque that has gotten down below the gumline is removed. This exposes the tooth surface to salvia, etc. and can make it sensitive to painful sensations. The plaque getting there to begin with is the problem. Tell your sister to use toothpaste for sensitive teeth. That should help in a big way in about 10 days to two weeks. She will need to floss daily to keep it from happening again, though.
It's very possible the same has happened to you. Plaque that forms along the base of the tooth pushes the gum away from the tooth surface. It forms a dental "pocket". Fluids can go down into the pocket area and transmit painful sensations through the tooth dentin which has now been exposed to the nerve. Toothpaste for sensitive may help you also.
There is also a distinct possibility that the tooth next to the questionable RCT tooth has a problem of its own.
Right now, your dentist sounds like he/she is taking the conservative approach. Healing from any dental procedure can take some time.
Both you and your sister need to brush at least twice daily for a minimum of two minutes each time with toothpaste for sensitive teeth. Then flossing once a day is a MUST to clean the dental pockets and help prevent gumline cavities between the teeth. It's the only way to remove plaque that will go down into those pockets and create pain.
Five minutes out of your entire day. Doing this will keep most future problems at bay also.
Good luck. Hope this helps.
My best to you,