Hi Amy, Congrats for getting to your goal! Technically, alcohol is not allowed until P4, as I'm sure you know. Does it matter to have a little now that you are 4 days away from P4? My guess it that, assuming you followed P3, your body will be okay It will affect you more since you are still low in calories. But probably out of ketosis by now. If you have the wine, I would have it with food.
Here's 2 reasons why I would consider not having the wine: 1) It will lower your inhibition and make it very easy to go totally off plan with food. Been there, done that. 2) You've worked hard to get this far & in hindsight you might regret not following protocol up to the very end. If that isn't an issue, great, but if it might be, then you should probably hold out for official P4.
I stopped P3 a week early because I couldn't stand the all-day famished feeling after the big carby breakfast. It still felt like a total success. For some, doing it 100.0000% by the book is what gives them the "I did it" feeling. Whichever way fits you, it is a game changer with your self image to know you got to goal having successfully completed the diet.
Long answer to a short question

Wishing you all the best with P4. Enjoy your celebration whichever way you choose! And be sure to celebrate your success every day!