For the sake of the devs, as to not draw too much attention to it, I won't post a picture or coordinates of it.
But yes, I can confirm that there is a Den in the upper right Deep Forest tile.
Oh? Interesting. I was sure that the devs would have hid it in one of the two backmost Deep Forest areas to make it as difficult as possible to reach. Although perhaps they are aware of just how frustratingly tedious the area is to traverse so they decided to throw at least a little bit of a bone our way. I will go there to explore myself for sure, thanks!
So, I can't say for certain, but I am going to make an educated guess.
If I remember correctly, the devs have previously mentioned that Acacia is so dangerous to justify the amazing loot you can find in the Deep Forest. And let me tell you, there is no loot whatsoever to speak of in the forest itself, which makes me think that her den might be a mini dungeon that you can enter, like the entrance to The Sunken Caverns. If that is the case, then then entrance should be in the exact middle of one of the Deep Forest tiles; aka [-200,400], [-100,400], [0,400], [100,400] for the 4 top areas, or [-200,300], [-100,300], [0,300] for the 3 lower areas.
However, if I'm just completely wrong, and the Den is not actually a cave entrance or some such, then I have found at least one instance of ruins in the Deep Forest that has the inside area of 8x8 tiles, possibly matching the "8 meters deep" part of the description.
That's where I'll leave my investigation for now.
Well, I can say one thing for certain; If Acacia has a Den, then none of the Deep Forest tiles mention anything about it.
I've been trying to get around for a while now with no luck, Acacia Always finds you.
I've heard that she supposedly sleeps, yet I've not been able to find an hour where this is the case. She's awake in the middle of the day, and awake in the middle of the night. And, of course, the NPC Editor does not allow you to edit her in any way.
You can only change the original NPCs into ones of the same gender.
However as far as I've figured, you can make it so the AI treats the character as the gender that you want by adding that detail in different ways, such as in the Public/Private Character Description, and in the character's Set Knowledge.
I don't know how far you have to go exactly, and the more stuff you change from the original NPC's original settings the more different they will become from their usual self.
If I ever were to try and find Acacia's Den's Coordinates, then I'd preferrably know her sleeping habits beforehand!
If memory serves me right, there is nothing at all on the map that indicates that there's any kind of civilization down to the south. Although it's been quite some time since I last willingly went down there to explore, so who knows. I think it's just in-universe lore as for now, just like with Thalassar at the end of the road to the right of Silverpine.
Thanks to Crayshen 's comment I went in to double check. Yes, the border counts.
So if I am in the Bottom Right of Silverpine, my position is [48,-49], and when I pass through the border 1 step to the right, being at the very bottom left of the map section to the right of Silverpine, my position is now [51,-49].
I will now go to the second area right of Silverpine to see if my position will end up being [101,-49] or something else.
So, I'm making a Silverpine Coordinates Map since I figured this might be useful if you want to make NPCs that live or travel outside of Silverpine for whatever reason.
I was just wondering if anyone better than me at math could double check that I'm thinking correctly when it comes to all possible coordinates within each square? Just so that I'm not making a mistake with the coordinates before I continue adding the rest of the coordinates to the image.
So like in the Silverpine square, the Player Character starts at coordinate 40,-1, the very bottom left corner has the coordinates -49,-49, and the very top right corner has the coordinates 48,48. This makes each square 98x98 tiles big, at least from what I've gathered.

The AI not talking about hair as much made me want to bring up another similar topic: NPCs telling me "Back So Soon?" pretty much every single day.
They do this even after me not having visited them for multiple in-game days. It breaks the immersion of me having gone off for a few hours or days, or even just going back home to sleep.