When using Setup Assistant the first time the new Mac is booted, you have the option to transfer data from a prior Mac and one of the steps allows you choose which user(s) to migrate. In this example (from Apple) there is only one user, but if there was more than one then you could select just one user to transfer.

If doing that, you'll be prompted to select a new password for her to be the Admin user on the new Mac. If the new Mac is already set up, you can use Migration Assistant to achieve the same result (the above screenshot is from those instructions).
Transfer to a new Mac with Migration Assistant - Apple Support
Personally, I prefer to do the above from a Time Machine backup of the old Mac on an SSD – it's very fast compared to WiFi and not subject to interruption by network issues. If you don't use Time Machine (or another strategy) to backup you Mac, now is the time to start for you and her. Drives come in two types, those that have failed and those that have not failed yet. A TM backup drive should be 2-3x your internal storage, and a 1 TB SSD can be purchased for <$100.