She can argue fraud, but that is a very difficult hurdle to clear. If she were to somehow prove fraud, then she could have the will declared invalid. So if you are asking whether it's possible, then yes. If you are asking whether it is likely, well there is no way to answer that given this type of forum.
I would strongly recommend that you contact a local attorney to protect your interests. If you try to do this alone, you are likely to find yourself in over your head.
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Only the person who made a will can revoke it. However, a close relative like a sister can apply to court to over turn a will for reasons like fraud, duress, lack of capacity, and undue influence although the burden of proof can be steep.
Lawrence Friedman, Bridgewater, NJ. Certified as an Elder Law Attorney by the ABA approved National Elder Law Foundation, former Chair NJ State Bar Association Elder and Disabilities Law Section, Member Board of Consultors of NJSBA Real Property, Trusts & Estates Law Section, Vice Chair Special Needs Law Section of National Academy of Elder Law Attorneys, and Master of Laws (L.L.M.) in Taxation from N.Y.U. School of Law. Visit SpecialNeedsNJ.com for articles and Q&A on elder law, special needs, wills, trusts, estates, and tax and SpecialNeedsNJ.com/blog for timely updates. Information on both Avvo and SpecialNeedsNJ.com does not constitute legal advice, as it is general in nature and may not apply to your situation or be subject to important changes. No attorney client relationship exists unless set forth in written engagement terms.
I believe this is a duplicate of your earlier answer. While the attorneys who volunteer on this site are very happy to answer questions and try to help you, it is not beneficial to simply repost questions, until you get the answer you want. You are in what sounds like a complicated situation and it sounds like the sister is not going to simply walk away. The only smart thing for you to do in this case is to immediately meet with a probate attorney to determine your rights and how best to proceed.
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