There's no blank portrait frame-thing in the L2 panel, she's just totally gone from there.
I believe Shadowheart's approval was at least high? I'm also looking at the
BG3 Wiki, and on her Approval page under Greetings it says:
Depending on their approval rating, Shadowheart may greet the player with:
...
Medium approval (20+) to Exceptional (80+)
...
After learning about Sharran worship:
"May the darkness protect you."
"Shar's blessing upon you."
"Lady of Sorrows guide us. Did you want something?"
I cut the irrelevant greetings from the quote, but she always greeted me with one of the Medium to Exceptional greetings where I knew about her worshipping Shar. Going back to my most recent save where she's still present, these are still the greetings she uses, and her approval is listed as High in the character sheet. I also never got a warning conversation from her before she disappeared.
As for Shadowheart's inventory, she wasn't carrying a backpack at the time but her items included her circlet, some Dark Justiciar Mail, and a Cloak of Cunning Brume, none of which ever showed up in my inventory or in the Traveller's Chest in camp.
