Yes, but you would have to tell the game to load the Elza Walker costume in place of the Military costume or one of Claire's four normal costumes, because there is something about the Noir and Elza Walker costume slots that makes whatever costume you use on them have holstered weapons disappear. I wish I knew why.
You can swap the Elza slot with the Military slot by creating your own mod with a file structure like
\natives\x64\objectroot\prefab\character\survivor\parts\pl1000\ and putting the costume loader files for Elza Walker in there + renaming them so the game loads Elza when you pick the military costume. So rename the three
pl1000_body/face/hair_costume_c.pfb.16 files so that they each say "costume_b" instead of c. Costume_a = noir, b = mlitary and c = Elza Walker. The Red Jacket costume is costume_1, 2 and default. You can get the official Elza Walker costume files and all other meshes and textures from the game by extracting the PAK files from your game directory using RETool (
see tutorial). The extra costumes are extracted from the smaller DLC PAK files.
The bad news is that she does not have a holster to put her gun in, nor a grenade launcher strap, so those weapons will just float on / around her. But hand grenades and knives will still appear on her back like this:
If you want it to have holsters, I'd recommend you create a custom MESH file of the red jacket costume and make another folder in your mod called
\natives\x64\sectionroot\character\player\pl1000\pl1000\ (the location of the red jacket files) to hold your edited model + its textures, which will then overwrite the red jacket when you install your mod. Import the official Elza Walker MESH file into 3D Studio MAX alongside the default red jacket costume and rename the Elza Walker submeshes so that they take the place of the appropriate submeshes from the red jacket. Then you should be able to select the submeshes from the Elza Walker costume along with the leg holster, belt and grenade launcher strap from the red jacket outfit and export them over the red jacket MESH file (tip: average normals on all submeshes you are exporting before you export). This will generate a new motorcycle suit costume MESH file with holsters which is technically a modded version of the red jacket costume.
To get the game to texture her motorcycle suit correctly, you will have to rename the three "pl1005_body_XXXX.tex.10" texture files (XXXX = albm, nrmr and atos) from the real Elza Walker costume from "pl1005_body" to "pl1000_jacket" (assuming you had the submesh for the motorcycle suit named submesh_1 when you exported, which designates it to be textured by the jacket textures). Then put them in your mod's sectionroot -> pl1000 folder. You will also want to move + rename Elza Walker wetmask file in there as pl1000_wetmask, instead of Elza's pl1005.