I believe this whole info like dependents, partners, co-signer etc will be only asked once you get selected to apply! On the form, name of the parents and/or grandparents only!
Oh ok! Thats a bit of a situation, because you cant sponsor hers and she cant sponsor yours, so I would say 2 forms would be require however, there is this all undertaking thing! Lets see if someone else had the same situation.
Do not resubmit, you can correct a mistake https://www.cic.gc.ca/english/helpcentre/answer.asp?qnum=1395&top=14 , they are asking to do not send duplicates! So I believe you can send an email to correct, or add a explanation letter later on
https://www.cic.gc.ca/english/helpcentre/answer.asp?qnum=1395&top=14
It says to send an email to the email on the website, explaining the mistake etc! Check the link!