I am so sorry for your loss and for the issue that you are having.  You may need to speak with a lawyer in your area on the matter. If your sister unduly influenced your Mother to change the Trust document when she was infirm in any way - mentally or physically - then you may be able to have it set aside.  But there are time limitations if Mom has passed to object to things and I fear that you may have passed the time to do anything. There are other issues with authentication of the note from your Mother and admissibility, etc.  Please go and speak with some one.  Good luck.