IMM 0008 is not for PR's, it is for non-PR's who are applying for PR for the first time.
When you apply to renew your PR card, use the forms here: http://www.cic.gc.ca/english/information/applications/prcard.asp but to explain how many days you have spent outside Canada, you can provide your own letters and documents to prove what you say.
However, you should keep in mind that they could refuse based on the fact that you have not been living with your mother, you have just been going to visit her 3 times a year. They could say that you could have stayed in Canada and visited her 3 times a year although I am sure it would have been expensive but in any case, they could say that the main reason you didn't meet the residency requirements was not the illness of your mother because if you did not even have to live in the same town as her, how much care did she really need.
Waiting for 2 years is much safer. Besides, if you were thinking that you could just renew your PR cards and leave again, think again. A H&C application to renew your PR will take even longer than a normal application and a normal one already takes several months. Add to that that you will still have to meet the residency requirements from now on, even if you get the PR card renewed this time. For example, if you are allowed to renew your PR card but then leave again and something happens to the PR card while you are outside Canada and you end up having to apply for a travel document, when they see that you had renewed your PR under special circumstances and then had left Canada again, they may well refuse the travel document.