by definition, personality disorder
start around teen age years, have been there for long time and need to be causing distress to either that person or others.
I can not see anything in your description of your sister's problems which make me think she has personality problems.
The recent change in her behaviour suggests that she must be having some stress because of which she has changed like this.
And I hope you are not medical too much the fact that she is being more devotional now. Praying to god etc is used as a kind of distraction from stress by many and I think we should give her some more time, if she is mature enough to understand her problems etc.
I think the first thing to do is to talk to her and try and find out why she is changed now a days, BUT IN A SUPPORTIVE MANNER.
OR ELSE, OBVIOUSLY A PSYCHIATRIC CONSULTATION WILL ALSO HELP CLARIFY THINGS AS SHE MIGHT FEEL COMFORTABLE TO TALK TO PROFESSIONALS RATEHR THAN FAMILY ABOUT PROBLEMS