stitching together several scanned images?

Think of your high resolution digital camera as a scanner.  Position your camera over you wife artwork parallel to the artwork plane of view. Evenly lite with a strong light source. Like full strong sunlight. Capture more than the artwork.  Use Photoshop perspective crop tool to crop to the artwork.  Use a good digital camera with a good lens.  Not your Phone.

A 16MP camera  file print at 150ppi will be good for artwork up A2 like a US 16" X 20" print. If you need larger  use a macro lens  capture the artwork in sections and stitch. Move the Artwork not the camera  capturing the images to be stitched.  Camera RAW and menu File>Automate>Photomerge can stitch your imaged in Photoshop.

It is possible to stich multiple images in Photoshop. To automate task, if I can understand you corectly, you must have 20% overlaping area. Overlaping means next or second scaned image which is lets say right side of entire image must have 20% of previously scaned part/image starting from right to left. Same thing for bottom parts if you must divide into 4 parts plus bottom parts must have  20% of top parts included.

If you can not figure out from my description search for explanation how to stitch panorama in Photoshop. If tutorial is using camera to capture images do not worry because image is image regrdless how it is created.

Another solution is to scan images then post them here so we can examine them and to give you advice how to stitch them.