You usually meet the passive candidate worth placing months before there is a role for her, and those months are where most recruiters either go silent or start circling like sharks. Neither gets a reply when the role finally opens.

How often should a recruiter check in with a passive candidate?

Three light check-ins over the months before a role opens keep you the recruiter she remembers: a follow-through in month 1, her own reason reflected back around month 4, and an honest market read around month 8.None of them asks her for anything.

Month 1, the follow-through. Send the article, the event photo or the introduction you mentioned when you met. It proves you listened, and it costs one line.
Month 4, her reason reflected back. When something touches what she told you, send it with one sentence: “Saw this and thought of what you said about owning something end to end.”
Month 8, the market read. One honest line about what you are seeing for people like her: which teams are hiring, what they pay, what they ask for. No role attached.

Why do these work when coffee chats do not?

Each one gives her something and asks for nothing, so she reads it as a person keeping in touch rather than a recruiter keeping a pipeline warm. The coffee chat asks for 15 minutes of her time before you have given her a reason, which is why she has learned to ignore it.

Each check-in also only works if you still have her words when the month comes round. The second one in particular is impossible without them, and it is the one that makes her feel remembered.