In the episode Scorpion: Part II Seven of Nine is separated from the collective when Chakotay uses a temporary neural link to sabotage the console she is using, permanently destroying her neural link.
Later, in The Gift
[Seven] is not used to being an individual and she repeatedly demands that she be returned to the Collective. Janeway refuses, and asks her to help with removing the Borg technology in Voyager's systems.
Seven threatens to kill Janeway when the Captain enters her cell in the brig intentionally unarmed. Seven even physically strikes her out of anger.
Why didn't Seven assimilate Janeway using nanoprobes when she was within striking distance? She had her tubules and her nanoprobes at that point and is shown using them for the rest of the series.
A couple of years after the above in the episode Inside Man; Ferangi hijack a hologram of Reginald Barclay in an attempt to send Seven's dead body through a geodesic fold so that they could harvest and sell her borg nanoprobes.
Also, in Body and Soul the Doctor is forced to upload his program to Seven's borg implants to hide from photonic (hologram) hunters. She uses her borg tubules to interface with his mobile emitter.
Further, the Memory Alpha entry on the Borg states:
Cybernetic implants were either surgically attached to the body or grown internally by nanoprobes injected into the bloodstream.
As she had these nanoprobes, what is the in universe reason that she gave up so easily and why didn't she attempt to assimilate the captain when she had the chance? She was enraged at the thought of not returning to the collective and reacted violently, why only that?