Why did your mom have access to your sisters account if you were the trustee? Time to see what, if any, methods of recourse you have against your mother, unless you want to bite the bullet for her crime.

That's when you direct them back to your mother? She wouldn't be able to get it out unless she could access it as well.

My mom stole money from me too. It was not a trust just a regular bank account and she was a cosigner. She drained my account and then over drafted the account. Didn't say a think till I went to cash a check and the bank ceased it. She stole my debit card that the bank mailed to me. I didn't know the bank was even sending it since the account was only suppose to be for checking not debit. I was a kid when the account was set up. The bank took my parents cards since they can't manage finances to save their lives. So my mom needed a debit card so they used mine without telling me. They would not close the account till I paid up which I did. Then before I could close the account the IRS seized all the funds in the accounts including mine because my moms name was on it as a cosigner. So my account was emptied twice. once by my mom and a second time by the IRS. I closed the account immediately and opened a new one in only my name. I don't give my parents money and I definitely don't let them know my account information. Its sad when my best friend is more trustworthy then my parents.

If she is a trustee, there isn't anything you can do, she has authority to make withdrawls. You might have grounds to press charges for fraud. If it was a lump sum, check with the financial institution for paper work required on a cash withdrawl of that size which will record information such as name, drivers licence, etc. That will be your smoking gun. Be sure to ask the lawyer who set up the trust about the possibility of restructuring the trust to take her name off. If you do restructure it, be sure to close the original account and open a new one.

Was her boyfriend a Nigerian Prince trying to reclaim his rightful throne?

That sucks. You may have to choose between paying back the money or filing criminal charges against you mom. Hopefully not.

Was she drunk when she made that decision?

Unless you also signed off on the withdrawal then I can see you being liable for what your mother did without your knowledge.

Oh no!