Some networks, especially state Medicaid plans, will suspend and/or terminate a provider's contract if the provider fails to file claims for over a year. So re-incorporating her tax ID won't mean a thing to them.
What you need to do is contact your major payers and find out what they have on file as the billing provider info. Billing provider info consists of tax ID, billing name (HCFA-1500 box 33), billing address (HCFA-1500 box 33), and billing NPI (HCFA-1500 box 33). You will also need to find out the correct PTAN (Provider Transaction Access Number) for Medicare claims. Generally if you call the main provider help line at Medicare and input the NPI, tax ID, and PTAN, then the IVR will tell you if the combo is on file.