As ML Orzel said, it is almost certainly a file type incompatibility problem.
If she’s trying to upload a picture, it is probably the default HEIF/HEVC format which is default.
She can change the settings in the camera settings to “most compatible” and then change it back later, but using a third party app makes this process super simple too.
Something like TurboScan makes this simple. It can produce whatever format you prefer (no affiliation).
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Scanner Pro (no affiliation) is another option.
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