If you renew your card before you leave, your application will be delayed and you will likely be investigated for not meeting the residency obligation.
If you leave Canada again without meeting the residency obligation you may lose your status when you apply for a PR Travel Document (PRTD) in order to return to Canada (because your PR Card has expired).
If you manage to travel back to Canada through the US (you would not need a PRTD in that circumstance), you may still lose your status at the border if they discover how little time you spent in Canada.
Basically, if you leave to take care of your mother, you will likely lose your status. Sorry, but that’s the reality of the situation.