She only visits the Freak once. Once, about three months after he died. She doesn't even know why, really. Most of her is saying that she should stay away, that he died and good riddance. But there's a small part of her that says that they need him (but they don't really, do they) and he's not there anymore. That he couldn't possibly have been a fraud. She argues with that part, he had to be; it had to be impossible to see the things he claimed to. But every time they get called to a case her resolve weakens fractionally. It's silly she tells herself. It was irrational to think that if the Freak died all the crime in London would stop. People keep killing.
But the papers had claimed he was responsible for all the crimes he solved. And the crime rate hasn't dropped since his death. Sally Donavon might not be a consulting detective or the British Government, hell, she's not even an army doctor, but she's not stupid. And if the papers got that wrong, what else were they wrong about?
She still believes he was a fraud (She has to. If he wasn't then she helped kill him.), mostly, but part of her wonders and it's that part of her that is the reason for her single visit. It's that part of her that brings a file on their current case, three drowned children and no leads, and after long minutes of internal debate it's the part of her that believes that lays the (illegally) photocopied photos at the base of his gravestone. Because three children are dead and they're turning up all dead ends and if by some miracle Sherlock Holmes wasn't a fraud, well they need a miracle.
"There you go, Freak," she finally says out loud. "You like the hard ones. So do us a favour and solve it."
She leaves it at that. It doesn't make her feel better and it doesn't mean she believes him or likes him or even misses him. But she's not stupid, no matter what he said, and if he isn't (wasn't) a fraud, they need his help.
A few days later a homeless woman comes in with a tip off that leads them to their killer just as he is attempting to drown his fourth victim. It crosses her mind to wonder, he was clever, fraud or no. But the tip came from a woman (definitely a woman, she knows the difference) and it wasn't a crazy deduction and they made the final link themselves, so no, he can't be. But from then on, whenever they get a tip off (and she does notice that more of them are leading them to the killers) she finds herself examining the person and the tip. Looking for any sign of the Freak in it. She finds nothing but that part of her that believes in him still wonders.
It never takes her back to his grave though. Once was enough.