As noted, you likely need to withdraw your app - it won't be approved even if modified. To be clear, the fact you have a child together, included her as common law on your app and submitted a statutory declaration does not make a difference - you'll need to demonstrate you resided together for 12 months continuous. It's still a good thing you included her as non-accompanying on your own app but it doesn't mean they 'approved' your common-law status.
You really only have two options under spousal sponsorship: marry and apply (inland or outland). Or, if she can visit Canada, reside together for 12 months continuous before applying - but note that's dependent on her getting a visa/entering Canada, and would likely mean ~two years before becoming a PR with visitor status.
Hence practically your best option really is to marry.
Note: you haven't specified and I'm assuming that there is no significant legal impediment to marriage. It would also be important to know if she has a visa to Canada/from a visa waiver country or has been refused a visa. (Won't get into this right now - advise if so, then it gets complicated)
I'm leaving out the possibility of her qualifying to immigrate on her own.