Going back to the game theory, this might be a strategy to energize Trump's base, but the more it's pushed the more it will also energize the left of the Democrats to accept her building biden's big tent for him.
I only know about Kamala Harris from the the primaries and there were so many candidates that quite frankly I got bored and overwhelmed with the process. But just from a perception standpoint Right now she seems to be rejected by the far left in the party and the more you say she's liberal the more that faction can justify voting for her
There's a quandary, because from what I've seen she's the Democrat with a track record of being tough on crime, so she should appeal to the moderates more. That means the Republicans have to try to make her seem more left leaning, which as you say could make her more appealing to the far left.
There's a couple of things to note though; most of those far left voters will vote for Biden as the least worst candidate in order to get Trump out no matter what, and also the far left are highly unlikely to take any notice of Republican campaign adverts anyway.
It looks like a solid strategy from that viewpoint (to an outsider with zero knowledge of Kamala Harris prior to her being picked as Biden's running mate).