Q: Mom and I got a joint checking account a year before she started to get bad. Is this account legally mine?

A: You are probably on solid legal ground, but anybody can sue anybody whether they can prove the legal right to win or not. Injunctive relief is permitted when there is an immediate irreparable harm that will occur if the court does not issue an immediate temporary order to stop another party from acting before a court can hear a dispute at a trial on the merits of the plaintiff's claim. I imagine the basis of the relief being requested is that you could spend all the money in the account before your sister can have a court decide whether the money is legally yours or belongs to the estate. An injunction in this scenario would likely be to freeze the account and preclude you from spending any money in it until the court can decide the case. Your sister must first prove that she has a strong likelihood of prevailing on her suit before a court may grant her an injunction. I do not know how she intends to meet that level of proof. Also, the ONLY person who has standing to bring a suit of this nature is the court-appointed Personal Representative of your mother's estate. Therefore, unless your sister is the PR of the estate, she does not have standing to sue and this suit should be dismissed (in which case, you should be filing a motion to that effect). If she is PR, then there is a statute that creates a presumption that a jointly titled account belongs to the survivor unless the account is set up otherwise. You should look up and cite this statute. Also, you are posting this for Maryland lawyers to answer, but I note you list New York as your geographic location. My answer is only applicable to a Maryland filed estate and/or a Maryland bank account, so if the estate or the bank account was opened in NY, you need a NY lawyer to respond.