Let r be the rate for Mia. Then the rate for Lora is 2r (as stated in the question).
Let the volume of the pool be V.
Then
V = 2r(16) + r(16)
V = 32r + 16r = 48r
rate = Volume / time
which implies that
time = Volume / rate
Let the time it takes Mia to fill the pool herself be t
Then
Therefore the time is 48 hours