Wendy walked 2 miles in 30 minutes. At this rate, how many miles could Wendy walk in 90 minutes?

Wendy walks 2 miles in 30 minutes, so she walks 2/30 = <<2/30=0.0667>>0.0667 miles per minute.

Therefore, Wendy could walk 0.0667 x 90 = <<0.0667*90=6>>6 miles in 90 minutes. Answer: \boxed{6}.