Yes for the credit freeze (all 3 credit bureaus) -- even if her state charges to set it up, it's a small price to pay compared to identity theft.
Yes for changing her phone number, unlist it, have caller ID, & tell Mom to only answer known callers.
In addition to opening a new checking account & closing her old ones, get the bank to not allow any auto drafts by 3rd parties.
Report the identity theft issue to the IRS & request a privacy PIN for her future returns.
https://www.irs.gov/newsroom/taxpayer-guide-to-identity-theftIf she has a Mac, set her up with two accounts: one with Admin privileges & one without. Have her use the one without. You manage the Admin one for access & updates you authorize. Or have her use an iPad.