Sorry to hear this. It's really rough when your Mom passes and you have to go through her things.
Guerrini is a really nice brand and that accordion appears to be in marvelous physical shape (on the outside). As Ventura said, many details are needed to make any kind of estimation on price. It's probably something she kept a receipt for which would help a bit. Still will need to know about reed configuration, bellows condition, the shape the reeds and keyboard are in, and general playability. Without opening the accordion up, there's no way to provide any assistance.