On the first day, she walks 200 + 300 = <<200+300=500>>500 steps.
The next day she walks twice the steps, which is 2*500 = <<2*500=1000>>1000
The total number of steps after the two days are 1000+500 = <<1000+500=1500>>1500
On the third day, she walks an additional 100 steps, bringing the three-day total to 1500+100=<<1500+100=1600>>1600 steps
#### 1600