Mavis had an average of 87 in 5 games of bowling. What would she have to score in her next game to raise her average to 89?

Mavis has played a total of 6 games (5 games + 1 next game).

To raise her average to 89, Mavis needs to score a total of 89 x 6 = <<89*6=534>>534 points in total.
Her current total score is 87 x 5 = <<87*5=435>>435.
Therefore, Mavis needs to score 534 - 435 = <<534-435=99>>99 points in her next game. Answer: \boxed{99}.