Most likely financial reasons, she can't afford staying in Australia for 2 more weeks?
Although according to the ITF site the hotel in Mildura for example is 65 EUR and in Moscow 90 EUR
And the flights to Moscow and back. Also, in Australia she would have excellent conditions for training in terms of weather.
Its because Mildura is on grass
Indoor hard suits Anett much better
And I think that she doesn't want to wait around to train on grass and then just go back when it doesn't benefit her season at all
I am not sure which one is a better choice, but if it is not inconvenient and I was her, I think i'd play Moscow too as it's like Yoshkar-Ola but nicer
EDIT: Moscow is really strong
I know she likes IH but I would have played Mildura as well
BTW, there are 2 grass court events that week
Neither in Europe