Screen time is screen time. It's great that she's playing a math game, and if it were me, I'd lump that in to screen time.
Do consider it her screen time, because although she's academically engaged, think about what else she could be doing. This is how I balance the idea of screen time in our house -- by what it takes my son away from. He doesn't play games on the computer, but gets around 1.5 hours of educational videos per week.
Screen time means that my son is *not* physically exercising/moving his body, which is vital to his health. He is missing out on actually sitting down and playing on his own, with his own imagination to lead him. These things actually improve his own problem-solving and personal skills like persistence on a deeper level. Child psychologist Bruno Bettelheim speaks to the importance of this sort of play throughout the book "A Good Enough Parent" and Community Playthings has a great resource handout entitled "The Wisdom of Play". Hands-down, open-ended child-led play is one of the best outlets and learning processes a young child can have. And during screen time, he is not interacting and playing with other children, which is also essential to a child's better development.
I personally think it's different than a workbook or reading because these have the potential to be more child-led, and children have the option of stopping, pondering for longer, taking a break in the page to think their own thoughts, etc. Screens tend to be more demanding and to lead the activity. Just my opinion. Also, the other (workbooks, reading) allow her to break for social activity. Games tend to draw the user solely into *that* world, and to pull us away from interacting with those around us. Workbooks and some reading (not all) allow for breaks for necessary social contact.
So let her enjoy that time with her game, and then send her outside on those nice days, and encourage that too. There are plenty of ways to explore math through play, too. :) Balance is everything!