I understand how hard it can be. When I first started calorie counting I had trouble calculating my own meals and I prepared them myself. I would also suggest finding a similar recipe online and going by that. In the future, if you want to calculate a recipe you can use nutritiondata (.com) It's a free site where you can create recipes and have them analyzed. It can be time consuming but once you have a recipe entered you don't have to do it again. Maybe next time you can ask to help your mom and just throw everything in a measuring cup before adding it to the pot

I would ballpark a regular soup bowl of the stew at around 350 calories depending on what she used to thicken it. Most recipes for soups and chilis with similar ingredients are around 300 - 400 for a large bowl.
I hope that is helpful
Amanda