I believe the marriage search is 5 years it cost $15 then after they provide her with the date of marriage if they find one she would have to pay another $22 to get the cert of marriage. It doesn't hurt to contact the funeral home since it doesn't cost her anything except for a little of her time and if they don't have the info that's ok it didn't cost her anything. You never know she might have had a sibling living at the time that provided the funeral home with the info.
I applied for a marriage cert for my uncle (by marriage) and was refused it because I didn't provide them with his parents names when I explained to them that is why I wanted the cert they still refused. I even had the full date of marriage. So that could possibly happen here. You never know with them.
That being said its really up to her to decided which is the next step.