In March, she walked for 31-4 = <<31-4=27>>27 days.
If she walks for an hour a day, the total number of hours she'll walk in March is 27 days*1 hour a day= <<27*1=27>>27 hours.
If each walk is 4 miles, the number of miles she walked in March is 27*4 = <<27*4=108>>108 miles.
#### 108