Aside from the time frame, and the word "sinister", that sounds rather like the beginning of The Diamond Age, or A Young Lady's Illustrated Primer, by Neal Stephenson.
In The Diamond Age the computer is a nanotech device in the form of a book which imprints on whichever young girl it's given to, and then educates her by creating stories for her to read and interact with.
The Primer in question is first stolen by Harv, who then gives it to his sister Nell. When the Primer learns Nell's name, it changes its title to "Young Lady's Illustrated Primer: a Propædeutic Enchiridion, in which is told the tale of Princess Nell and her various friends, kin, associates, &c.". It's able to figure out that she hasn't learned to read yet, and starts by teaching her that. By the end of the novel she's learning computer science and nanotech engineering, and has in fact found the blueprints for the book itself.
As for whether the bond between the Primer and its owner is sinister... I'm not sure the word fits. "Disruptive" would be a better word. The design purpose of the Primer was to empower its owner through education, but specifically by teaching the owner to be subversive. By this the originator of the Primer seems to have meant that the Primer should teach its reader that they can change the world. All of the girls that receive a Primer end up doing this one way or another. One rebels against her parents and falls in with criminals operating a dark net, another rebels to a much lesser degree, runs away from her mother to join her father on a quest and then becomes an actress. Nell doesn't rebel, but she does get into some trouble. She's probably closest to what the originator of the Primers had in mind, since she becomes a leader (also an engineer, a warrior, and a head of state).
On the other hand this was published in 1995, which doesn't fit your time frame.
Voice synthesis in this story exists, but the voices of real humans are always preferred so there's a large industry of live actors to play the NPCs in interactive entertainments. For a premium you can also pay to join a multiplayer session with professional actors. The work is farmed out in a system much like the Mechanical Turk; all the actors are essentially anonymous and even their voices are tweaked in real time to better fit the character. The Primers can use both systems, and their creator pays all of the bills.
Miranda, the actress ("ractor" is the term used in the book) who happened to get an early contract to read some lines for Nell, recognized that the content was more interesting than the usual children's entertainment and opts to keep receiving them whenever she's available. She spends more and more of her time reading to Nell, then changes her schedule away from the prime markets (the Greenwhich and Eastern Standard time zones) to read to Nell more often. Even though she doesn't have any control over what the Primer is teaching, she can hear Nell when she speaks to the Primer, and so learns a great deal about her. The story covers at least 14 years, and Miranda spends so much time with Nell that she first gives up her acting career, and then even more, to try to penetrate the anonymity and reach Nell. Once Nell starts learning how computers work she suspects that Miranda exists and likewise seeks her out.
The other two girls who receive a Primer don't form such a strong bond with anyone, though it's not entirely clear why. One of the girls is bratty enough that she might have unknowingly turned off everyone who took the job. In any case, the influence of the actors might be secondary; they have no control over what lines they end up reading, since those are created by the Primers. There's a very powerful scene where Miranda finds that Nell's latest "stepfather" is particularly abusive. The Primer begins to tell a story about how Princess Nell ran away from an ogre, and Miranda tries to get Nell to run away as well, putting all of her emotions into the lines she's reading. When the moment of crisis comes, Nell just says that she knows what she must do and leaves, leaving Miranda alone in her room in the theater not knowing whether Nell is even alive.
And of course I'm leaving out everything to do with the Mouse Army so that I don't spoil absolutely everything.