Shes giving you money, or you're proposing to use your TFSA room to shelter her money? That sounds like a bad idea for a myriad of reasons, for starters it's likely on the edge of tax law.
If you are close to mortgage free, why would you not be planning to max both your own TFSAs? $5500 ex-mortgage money fills pretty quickly.
Please come back to what they should have done before he passed - did they only have one TFSA account, plus a taxable? Need to know what to help my parents avoid. Thanks.