You have to submit every single document at the same time to USCIS. The marriage document has to be included with the petition. And the marriage has to be legally recognized in the country in which it occurred in.
Also, if your marriage certificate is in any language other than English, you have to submit a translation of it. And you are not allowed to do your own translation. I had to have my husband's birth certificate translated.
For example my husband and I were married in the US so our marriage certificate is valid here in the US. However it would not be valid in Germany because of the Haute Convention unless we had an apostle (the secretary of state in whatever state you marry in) sign off on an additional form. Our marriage is 100% legit and recognized in the country in which we were married so it doesn't really matter that it isn't recognized in his country.
I just submitted my I-130 petition to USCIS last week. I hired an attorney to handle my case for me as there is going to be a red flag on my case due to the age gap between my husband and myself. Anyways, if your wife would want the help, I would be more than happy to help her with all the documents she needs to gather to submit to USCIS.
I'm offering help because it would be nice to have someone else to go through the process with.