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Don't respond to any text messages that do not directly relate to a family get-together, positive messages or something else perfectly normal. If you are getting texts that spell out her outrage about things that have happened to her, her annoyance at something you've apparently done or to send you gossip about family or friends, let it slide and leave her wondering. If you feel angry and want to send back a retort, reprimand or justification straight away, don't do it. Treat your anger or irritation as a warning sign to sleep on the matter. Furious texting or messaging can only end in more angst on both sides. If your S-I-L is truly a pain and a bit of a drama queen, it's possible that her social networking reflects her attention-seeking ways. You can be all too easily drawn into a web of her anger and drama venting if you can see her Facebook updates or her latest tweets.  If she friends you, you can do one of several things.  One, simply ignore the request. When she asks you about it, tell her that you don't use social media much to exchange important things (or at all); or Two, reply to her with a "Thanks but no thanks, I am not accepting new requests at the moment due to busyness/privacy/overloading, etc." You might also add something like, "Besides, we see each other often and I prefer we talk face-to-face"; or Three, turn all of your settings to private so that she can't see who you are friends with. Either say nothing or tell her either that you stopped using social media or that you only have a tight knit circle of followers and don't wish to extend it at the moment. If you say you didn't receive any request, she'll only resend it, but it might buy enough time to throw her off the whole idea if you offer to "look into it" but let the "looking into it" drag on and refuse to raise the matter again); or Four, offer her a more neutral alternative. Offer to friend her on Pinterest and focus solely on a shared craft or cooking board. Nothing racy or mean spirited, of course.   Try to avoid using the terminology of "friends" when discussing any refusal to accept her request. Unfortunately, the usage of this term by social media sites has caused many people to take it at face value; many people are simply followers or fans, not friends. She might feel devalued if you make any suggestion that she is being rejected as a "friend". If she is already a follower of one or more of your networking sites, you might consider blocking her and turning your pages private on some sites. Most probably you will need to explain what has happened (with a sound excuse); if she's a drama queen, she'll not only notice but she'll take offense too. If she acts abusively, it is recommended that you keep records to show your spouse and other family members if needed. Save messages, emails, voice-mails, etc. Some drama queens like to "attack" when nobody else can see, thinking you won't have the courage to out them. This isn't about deliberately looking for dirt but it is a way of protecting yourself if anything should get out of hand. However, this is truly the stuff of last resort––if you handle yourself deftly in public situations around your S-I-L, everyone will know for real who is behaving and who is stirring the pot.
Avoid answering what isn't worthy of a response. Keep social media networking to a minimum with your sister-in-law if she sets off your buttons. Take care if you do soldier on and try to be her friend online and/or through the phone.