A spousal visa, processed through USCIS, NVC, and the consulate, could take about 2 years. The I-130, alone, at USCIS, will take a year or so for approval.
My decision process for a spousal visa:
Step 1: Decide when you want to re-locate to the US.
Step 2: Decide if you want to try the DCF route (if petitioner is living outside the US) or if you want to file normally thru USCIS.
Step 3: For DCF, contact the consulate and request they process the case. If approved, they will give you instructions for filing directly thru them. For normal consular processing, you file the I-130 thru USCIS. Once you file normally thru USCIS, you cannot later file DCF.
If filing a normal I-130 case through USCIS, see this guide:
No... ...If you file an I-130 online to USCIS, you lose DCF........DCF means "Direct Consular Filing"......Filing online to USCIS means consular filing....but not DIRECT Consular Filing. With DCF, everything bypassess USCIS.
But, for consular filing (filing an I-130 thru USCIS), you would put that your consulate is Montreal....but that is not DCF.
Be aware that you cannot go the DCF route once you have filed a normal I-130 with USCIS. Also be aware that Montreal is notorious for their scrutiny of US domicile.
Of course, they can....if the consulate officer believes the petitioner or joint sponsor has sufficient income or assets to prevent the immigrant from becoming a burden to taxpayers.
Under the law, Petitioners are responsible for supporting the immigrants they sponsor...If consulate officers think the immigrant is likely to become a burden to taxpayers, they can deny visas or require well-qualified joint sponsors.
Actually, I am surprised we don't see more public charge denials. I don't recall seeing one in a couple years.
I would not withdraw and refile yet. I would wait. The I-751 was filed under her A-Number. Assuming you filled in the I-751 correctly, I think she will receive the extension letter.