If you cannot have access to her "finances," how did you prepare a joint tax return? You would need her W-2s, 1099s, and other financial documents or information.
I'm not sure exactly what you mean by "signing the tax return on TurboTax." If you are e-filing, you each "sign" the tax return by entering your 2020 AGI, which is the same for both of you if you filed jointly for 2020. There is no written signature on an e-filed tax return.
There is no way to give someone limited access to your TurboTax Online account. If you give your ex access to the account, she can do anything that you could do. What I would suggest is that you send your ex a PDF or printed copy of the tax return for her to review. That way she cannot change anything. Have your divorce lawyer prepare a document for her to sign, authorizing you to electronically "sign" the return on her behalf for e-filing.
