Removing Salsa flavor from vegetable soup
First off, you may want to consider starting over. You have 2 big problems, and you could end up spending a great deal of time (and ingredients) trying to fix it and end up with something twice as big and just as unpalatable. 

If you really want to do it the salsa part is easy: cook it. What many people don't like about salsa is raw flavors, they will mellow quite a bit with the application of heat. If you don't tell your daughter then chances are she won't even know! 

The real problem is the salt, once you add it there's no sure-fire way to get it out. If something is very salty the only thing you can do is add ingredients that aren't salty in order to even out the salty flavor. You could make another vegetable soup with no salt and then mix the two, or add some water to your soup and see if that fixes it. 

If it isn't too salty I have had some success using potato to absorb some of the salt. Potatoes are good at soaking up salt flavors, you can add some cup up potatoes in and once they are cooked take them out and some of the salt comes with them. Or if you find that the combination works leave them in. 

So what I would do is if it's not too far gone would be to add some unsalted stock or water, and then some cut up potatoes. Cook it until the potatoes are tender, then taste. If it's acceptable then serve it with a smile, if not throw it away and chalk it up to experience.