Bella uses one of the ones that Sherlock gave her and pretends she bought it with the money her father gave her to pick one up. She can always use a little more untracked cash to buy magic things.
Her newt skeleton comes in.
She casts every part of the spell except the final act of will, which she can do any time, anywhere - the spell was effectively on her, to turn her into someone who can at whim destroy the Gem of Amara. She doesn't do it. Sherlock's harmless, and he still - apparently, given that he shows up at school - has the gem.
She can, sort of, trust him. Mint oil and divination lens, useful things.
She's not sure she can forgive him, but she doesn't have to forgive him to not want him to die.
"I'm not sure I agree with your premise. If I say the data doesn't exist, and you think it should, why must it be my skill or my architecture that's at fault and not my circumstances?"
"I think my ability would remain intact, if perhaps diminished, even in the data-impoverished situation you're describing. Given privacy and paper."
"I write, with absolute, unflinching, honesty - albeit half in code, for all that I trust my parents to respect my privacy - so my thoughts don't escape. Occasionally there are diagrams."
"I wouldn't think mine were either if I didn't go around with a metaphorical butterfly net over my head."
"Conversely, I'm not sure I could write them down if I tried. They don't come in the right format, by and large."
"Maybe it's architectural, or idiosyncratic, or otherwise non-transferable. I don't know. It doesn't sound like you're interested, anyway."
"I am interested. Observe my interest," he says. "But I do think it's idiosyncratic in some way, because some part of the process is still lost on me."
"It works very well for me. I've never tried adapting it for anyone else; maybe I'd have to know more about you."
"Observed data, connections between same. Feelings. I do have some thoughts in words, they're just - unbelievably slow, compared to the rest."
"I'm not immediately coming up with a faster encoding mechanism than writing," she says. "I mean, I guess typing could be faster if you had a decent typing speed."
"What I'd really like would just be directly perfect recall. But I can make paper work."
"Mine is generally obedient. But I've heard of things like mind palaces, for storing a lot of information where you can get at it whenever you need to."
"The advantage over notebooks being? Besides the obvious ones of portability and privacy."
"I don't know how it compares on storage speed, but retrieval speed has got to be orders of magnitude better."