It is not possible to apply for a Super Visa from within Canada. CIC Call Centre agents are never too sure about even the basics.
You can only apply to extend her visitor status (on a regular TRV) for up to 2 years if she is already in Canada. This is called 'Authorized Period of Extended Stay'.... which most people tend to confuse with a Super Visa.
If your mom is from a visa-exempt country, she must apply from for a Super Visa from her home country..... she will have to go through medicals and other requirements. If approved, she will get a letter stating that an eTA is issued to her.... and her stay for up to 2 years (upon initial entry).... will be decided by the immigration officer at the border
