Yeah it actually worked! Thank you really much!Just checked your save. Seemed to work just fine for me. Seen you already had Kim's skateboard and Gwynn's unlocked. Clicked on her outside, seen the scene and had the option.
Now, I THINK I know of the problem. I may have ran into it in testing, but running mod tools to super skip scenes, I couldn't figure out if I fucked up or just missed something. I changed the quest variable of gwynn's questline to something else and I have it fix after you load into the game. Now, I assume you're going through this in one playthrough? If so, then maybe that specific variable isn't getting changed until you restart the game, and that's why it worked for me, I started the game up with your save.
So... essentially, just restart the program and load in the save you sent me and go to gwynn's house. I bet she was never outside for you and the door was able to be used to visit her. It should have barred you from going in.
edit: from what I see, if you don't load in at any point between returning to the present and now, it causes the problem. I've fixed the problem though!
TL;DR - Restart the program, load in your save and try again.