In short, this mod marks Deirdre as Protected (just like all the other special Slog settlers), and makes her actually sell items like she claims to do.

I assume that most people who have played Fallout 4 have encountered the lovely ghoul named Deirdre. However, just earlier today, I got a report that someone who has played this game for an entire 1o,ooo hours, with over 6,ooo mods installed at a single time, has never met Deirdre! Incredible, no? Downright unbelievable. So i'll take just a moment to introduce you to her.

Deirdre is a named settler who lives at The Slog. However, she is broken. She's been broken since Fallout 4 debuted. There are two small... oversights? about her.
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First - she is supposed to be a vendor, like the other few special vendor NPCs found at other settlements in the game. (Connie Abernathy, Supervisor Greene, Daniel Finch, June Warwick)
She has special dialogue claiming that she will sell everything a wastelander needs, but most people will realize soon that she never actually sells anything.
This is because her vend-ability has a condition check that's backwards. The condition checks for whether the player is the owner of the Slog workshop or not. Because the condition is set to 0, Deirdre only actually functions as a vendor BEFORE you claim the workshop. This is simply fixed by changing the 0 into a 1. Now she'll function as a vendor AFTER you claim the workshop.

That's not all though - there seems to be two separate vendor lockers for The Slog. In one locker, there's only 5 tarberries, and the locker does not respawn. If you were to take all those tarberries out of there, it would never restock. In the other locker, it is fully stocked with all the things that Deirdre claims she'll sell to you. However, the second locker is not linked to Deirdre. It's not linked to anything. So, I simply copied the stock from that unlinked locker and pasted it into the locker that's linked to Deirdre, and set it to respawn like all other vendor stocks in the game.

Second - she is mortal. All the other Slog settlers (most special, named settlers in the game, actually) have been given the Protected flag. However, for whatever reason, Deirdre never received this flag. This means she can easily die, whereas every other special, named settler will just take a knee and enter a bleedout state whenever their health hits zero. With this mod, she will now have equal treatment.
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Huge credit goes to robotized as they're the one who found the guilty 0 and turned it into a 1. :D
This mod is incredibly light, and can safely be installed or uninstalled mid-playthrough.
You can install it manually if you like, or use a mod manager of your choice.
The file is an ESP marked as an ESL, so it won't take up one of your 255 plugin limit slots.
No requirements on any DLCs or mods, and it uses no scripts.
However, the Protected flag that this mod gives to Deirdre will conflict with any other mod which alters Deirdre.
Due to that, you'd be best to place this mod beneath any mod which alters Deidre, if you have any. (the only mod I have which touches her is NPC Level Scaling)
It's not a big deal if you don't place this mod correctly in your load order, though. If you are comfortable with Deirdre staying mortal, the rest of the fixes introduced by this mod will still function properly. She'll still be a functional vendor.
...Unless of course you have a mod which alters the Slog vendor locker specifically. Which would be outrageous.