Honestly, spell focus can be a rather cumbersome thing in 5e, but it's not meant to be. In Solasta, it is one of the things I didn't like. Kinda a pain in the butt. You can't just cast a spell. You have to have at least one hand free.
Spell focus can be any number of things. A crystal ball, a necklace, Shadowheart's circlet, etc. I think it should be less cumbersome than Solasta. As long as you equip it somewhere, you can cast spells. So, SH equips her circlet and she can cast her spells. She doesn't require a free hand.
That said, Solasta ticked me off in that it didn't warn me. I accidentally sold my cleric's spell focus, thinking it was a different amulet, and suddenly she couldn't heal anyone. If they do decide to do spell focus, they should at least warn players, "If you remove this, SH can't cast spells. You'll need to equip another spell focus somewhere."
