Welcome! This is an online support group for anyone who is very afraid of dentistry or who suffers with dental phobia. Please note that this is NOT a general dental forum! You can find a list of them here.
I have had many fillings on 2nd molars, but it really depends on the condition of the tooth. A dentist should be able to tell her if the tooth can be filled or if she requires a crown or a root canal. Sometimes, the dentist cannot tell until they start working on the tooth. Hope this helps.