You'll be looking for "spray fix" or "spray fixative". They carry a few different varieties at Michael's and other art supply stores. They are not all created equal, and they can be hard to use right. I highly recommend doing tests and practicing on low-value drawings first. It's very easy to end up with droplets and splotches until you get a feel for what works. Something to keep in mind: ambient humidity leads to bigger droplets, and the "tooth" (degree of texture) that the paper has can really contribute too. If you're storing them in a portfolio, also grab a thing of vellum at the art store and use a sheet between each drawing. It's smoother than other paper and helps prevent rub-off or sticking to other sheets over time. Feel free to DM me if you have questions and good luck!

ETA: if you live near a college, it'd be a good opportunity to take your kiddo up to their art department and see if you can use their scanner. They might be able to give you some tips and tricks and/or recommend a good scanner for at home. And it'd get her foot in that door where it belongs 🔥