Thinking about avatar's and yes I agree this is not one, in that their is no need to 'tend' it as you do with such things in the gaming world, here I'm thinking of those Japanese games (with Mudkips and shit) and things like The Simpsons (video game). These things are so popular (I'm not a fan but know of them), because people end up identifying so strongly with the avatar, characters that they have to feed etc. Here the cookie is a pretty life-like simulation, that is autonomous, after the training as Alan_F pointed out and this puts distance between the simulation and Oona Chaplin but she was aware that a copy of her of sorts was being created to make a smart appliance app (something that is already here, you can programme a lot of the stuff they did in the show, with smart appliances). So for Oona Chaplin there was zero empathy with something even more lifelike than the stuff video games hooks millions of people on. For most of us, if we had a simulation of a copy of ourselves trapped in some cookie, we'd be like hey dude how you doing in there, can I put the Liverpool match on for you? get you some virtual beer? how about some virtual babes and cocaine etc..? You would, like in the gaming world try and make life as great as you possibly could for the almost identical copy of essentially yourself. Of course a lot of people play things like The Simpsons just to get a joy out fucking things up...
I don't think it is that big of a deal, the show was still great, everything fitted together and when you are working at the level of ideas like Brooker is, you allow him a little suspension of disbelief on the part of the viewer.