Odds are you've run across a few overbearing people in your life who thought they knew it all and were in some way superior to you. If you were lucky you weren't related to any of them and could easily exorcise them from your life. Unfortunately, if this overbearing person happens to be your sister, it isn't as easy as ignoring the problem or cutting off the relationship. While you're unlikely to change this behavior in her, you do have total control on how much you allow it to affect you.
Talk It Over
By caving quietly to this behavior you enable it to continue, which only fuels the long-term conflict and ultimately robs any authenticity from your relationship with your sister. Be honest about how this behavior makes you feel. Use words like, "I feel," rather than the more incendiary comments that try to attach blame like, "You make me feel." Even after talking it through, your sister may try to wrestle control over manipulating your emotions. Agree to disagree and let it go.
Boundaries establish that there are parts of your life where you hold the final authority. If your overbearing sister has to have her say over how you conduct your life, it then defaults to you on exactly how much access she has to your personal information. Decide that some things are simply off limits, even for family. If she meddles into your love life, keep the intimate details of who you date to yourself.
Don't Play the Game
Overbearing people expect you to submit to their behavior, possibly because you always have. These are patterns, particularly with family members. Maybe your sister is older and used to being a parental figure who keeps you cast in the role of a child. Recognize that she uses emotions like guilt or shame to dig at your self-esteem so she can keep her control. Ignore the triggers to fall back into old patterns by taking responsibility for your feelings.
Get Some Distance
In the end you cannot change her, only how you react to her. Her actions do not have to reflect on you. If they do, perhaps there is something inside you that needs to be addressed, like an underlying unmet need that leaves you susceptible to a controlling, manipulative personality. Sometimes you have to get some distance, whether physically or emotionally, until you become strong enough that you won't fall prey to the overbearing behavior. Then you both can find balance in a healthier relationship.