Thank you for sharing your mother’s situation and question with us.
According to several CIC representatives, if your mother’s application was signed by her more than 90 days ago, then she will need to complete a new form.
However, if it was signed less than 90 days ago, she can simply complete the highlighted portion and resubmit the original application.
We suggest that you contact the Citizenship and Immigration Canada (CIC) Call Centre directly for information specific to your mother’s application and for confirmation of this information we have provided you.
I hope this information is helpful. Please let us know if you have further questions and if there is any follow up to your question/situation.