If you pulse it a food processor does a perfect job with salsa. I also use canned tomatoes....because I LIKE it made that way (LOL!) but I use whole tomatoes...and often quickly pulse and remove...and do the same with the green peppers and the cilantro and put the 1 MM slicing blade in for the green peppers.
But...if I am only making a small amount of salsa I will just tear up the tomatoes by hand and chop the veggies with a knife.
Linda C

Your blender will work fine, the only difference between it and a food processor is that it doesn't have a pulse. You can pulse it by hitting a slow speed then off, push the big parts down and do slow speed again. Keep doing that for each ingredient and you have ingredients.

My guess is that your SIL's salsa is so good because she uses fresh tomatoes. Canned is good for a lot of things, salsa isnt one of them.

Have you seen these? My friend started using one of these years ago to make salsa. She was living in CA and really into making mexican foods. It's not electric so you can really control how much the food gets chopped.

Here is a link that might be useful: salsa chopper

I did 10 litres of salsa from fresh tomatoes and peppers. Sliced everything by hand and blanched the tomatoes. The texture is super nice so I'd say that a good knife is your best bet!