Little bit of steam help
Little bit of steam help
I don't recall how it was originally configured. However, your sister appears to be unable to play any games in your library while you're using them, whereas she could play a different game. It seems the feature isn't available anymore. Would there be a way to re-enable this or is it removed? You mentioned you want to play different games you've purchased, such as Mord and PC Builder, and Beat Saber specifically.
The Steam family sharing lets you access the same library on different PCs, but it never supports simultaneous play for everyone. Only one device can use it at a time; after a short delay, others receive a warning and disconnect. To work around this, switch your host PC to offline mode. Then both of you can play freely, though multiplayer games will stop until you return to online.