Starter kit for a teen

I can highly recommend darktable http://darktable.org

it is not basic, but its approach is one that allows the user to learn about what the software does.

You can use it to do just simple things like cropping et al, but it also lives up to a professional workflow.

Let her play with that.

Running a linux system (which darktable runs on), she would probably find that her laptop isn't underpowered at all, but her current operating system is just overly heavy.

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Richard