what I used to do when my sons were a bit younger was to rip in both flac and mp3 for all their albums, whether they asked or not. I have a ripper that does this simultaneously, which dumped the mp3s in a network folder they could access, so it cost me nothing in time just a bit of storage space. You can add the conversion step as part of your workflow, through JRiver directly, just a 2-step procedure. That way no issues.
Now they are in their 20's so I just let them go in via Teamviewer from wherever they are and take what they want. But they are savvy geeks, with good taste. I actually want to rip their albums for myself
Not exactly what you want to hear, but short of creating a local library for her and having her pc run another version of media server, can't see away around it other iirc route recommended by Mattkhan, can't think of much else.