"What do you do? Keep on believing, because does it really matter?"
Perhaps look to see if you can find if this other woman has married someone else or died without marrying? In that situation it would be clear that she isn't your ancestor.
"A newly released parish record set..."
So it sounds as though the two women were born (and maybe lived) in different villages or towns. I'm guessing here that "your" ancestor was on the records of a different parish?
Did any other marriages take place around the correct time in nearby villages that could have been that other woman?
Alternatively, you need to look at DNA if you haven't already done this. If you have DNA matches that are related to you through the major player family then that is evidence that your original belief was correct. In contrast, if you find DNA matches that you are related to through this new woman's family then that will point in the other direction.
One thing I will say (and this has really helped me a lot) is that if you have people from your parents generation (or even grandparents) still alive then it makes it so much easier to find DNA matches as you have an earlier generation of DNA.
On Ancestry I have around 16,000 matches. But my mum has 21,000 matches and my dad separately has 18,500 matches. So, by going back an earlier generation I have gone from having 16k matches to 39.5k (21+18.5). So the number of matches has more than doubled for me by going back one generation.
This really has helped me in a number of situations.
Just to give you one example that is, I think, very relevant to your situation.
In my family, there were two cousins, both named William, both born in the same small village one was born in 1754 and the other in 1755. They then both went on to marry women named Mary.
When it came to the Mary's there were, like in your situation, a couple of different Marys that it could have been (no one from that village with the name but from nearby villages)
There were some DNA matches that linked back to my mum through the sibling of one of the women that it could have been. We could find no links back to the other woman of the same name.
So, it is most likely that it was the woman through which my mum is a DNA match with these other people is the actual one who married one of the cousins.