Dealing with a jealous sister can be a daunting task for any family member. Add unreliability to the mix and you've got a recipe for disaster. A jealous and unreliable sister can make you feel guilty for what you supposedly don't do for her or what you have. She can drive you crazy by making promises she won't keep or not showing up when she says she will. Learning to deal with a jealous and unreliable sister can be extremely challenging, but there are several things you can do to help yourself through the process.
Recognise the limitations you have over what you can control regarding the situation. You have the power to control your reactions, but you can not control another person's actions. This might be a bitter pill to swallow, but the sooner you recognise that you will not change a person who is not willing to change, the better.
Talk to your sister about how you feel and what you see as far as her behaviour goes. She may not realise how she is acting or how her behaviours are affecting others around her. Talking to her and pointing out how she makes you feel may be enough to help make changes in her behaviour.
Do not allow your sister to guilt you into things, such as giving her clothes, money or other items she covets. Jealous people tend to use guilt as a means to gain what they want. Tell yourself that you have worked hard for what you have and there is no reason to give it away, especially to someone who would use guilt as a means to get it.
Do not ask your sister for any favours unless you want to hear her say, "Well, then you owe me...," as this will be the likely result. Do not rely on her to do things for you, as she will likely not show up or have an excuse as to why she suddenly cannot help.
Keep contact with your sister minimal, but cordial in order to prevent family fights or discord. The less you interact with your sister (if she is not willing to hear you out and make some changes), the less strife there can be between the two of you.
Attempt to address the behaviours again if no changes have been made over several weeks or months. Your sister may be going through some hard times and need support, but she also needs to realise that her jealousy and unreliability are not ways to go about asking for and receiving help from you. If you want, tell her you are willing to help her, but only if she changes some of her negative ways.
Cut off all communication if things get out of control or you feel threatened in any way by your jealous and unreliable sister. You need to think of yourself and your family first and foremost, and cutting ties with a sibling may be the only answer you have.