Unfortunately there is not much any attorney can do on this site for you because you are looking for legal advice not just a simple question.
You have to respond to the petition and object. See probate code Section 15642 which sets forth the grounds for removal. If the trust provides a life estate to you, then you have to set that forth clearly for the court. Are you maintaining the property, keeping the property taxes current, keeping the property insured? You need to look at the law and facts that she cites as the grounds for removal.
How did she put the house on them market? Is she a cotrustee. You might want to seek out the assistance of a organization that provides legal services such as a legal aide group.
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Work with an Estate Planning or Probate Litigator to get this problem resolved. You need to appear in Court and get this going right away. See Avvo.com under Find-A-Lawyer. Good Luck!
You'll have to file an objection, which isn't just a form but a document entirely created from scratch. It will look similar to the petition she filed to remove you.
The only way I could see that she would have a case is if the trust required you to continue to maintain the home (pay the property taxes and upkeep) as a condition to your life estate and you've failed to do so, however, it sounds like from your description she tried this first and lost.