Never got around to posting this! I didn't do much and there's not much change; I just wiped down with vinegar and moisturized with Blackrock (two coats) and Leather CPR (3 coats?). I think my biggest successes were lightening up the water stain on the bottom and getting the bag back to its original structure. I used a cotton round to saturate the whole bag with vinegar, and let it air dry. I worked with a panel at a time just to make sure it didn't get ruined. I tried to avoid wiping because I was scared of removing too much red dye. Getting rid of the water stain took a couple of tries with the vinegar. I got it to reshape by completely stuffing it while it got soaked and dried in vinegar and later conditioner, and I left the stuffing in for days even after it was dry from everything. After vinegar soaking, I realized there was not much more I could do about the darkened spots so I just moved onto conditioning. I still think it could use another coat or two - still feels a bit parched!
Anyway, here's a before picture of the loose structure (from the original Etsy listing), and of the water stain. And then pictures of the after, plus how I plan to style it (with my belt bag around the waist and tiny shopper in hand!)

It's weird how it looks intensely red in some lights, and more subdued in others! I love how you can see the natural striations in the shopper's leather. And you can really tell the shopper is a much older lady than my belt bag haha. If anyone has tips or comments, I'd love to hear your thoughts!