My brother changed his direct deposit check now its going to the wrong account. How do I stop it?

It sounds as though when you went and changed his direct deposit information nobody thought to change his online SS account info and password so it was easy for her to change the account back to her own. You need to contact SS asap to tell them his account has been fraudulently changed and you need to speak with someone who can also block this woman from any online accounts she may have access to (I would check his bank accounts too). Sometimes they can work with you by phone if he is able to provide identifying info and give permission for you to speak on his behalf.

Get his login and password for SS. Change the password.
Do the same for his bank accounts. Sit down with the bank manager and explain the situation.

Star, could you please tell us who is "she and her".   Does "she" have Power of Attorney" for your brother?

Sounds like "she" has set up an on-line account with Social Security for your brother and any time the direct deposit goes elsewhere, "she" is able to make the change back to where "she" wants the check to go.

You need to call Social Security and explain what is going on.   Maybe they have someway the on-line account can be locked after the correct direct deposit location is set.