Right they have her back nearly 6 lengths after 3/4, but a little over 8 1/2 after the mile, meaning she closed that much in 1/16 of a mile. The final 1/16 was run in 5.82 seconds. If you use the assumption that 1 length is approx. 1/5 of a second, she ran 1.7 seconds faster than the leading horse for the final 1/16, in 4.12 seconds. This translates to a 8.24 clip for 1/8.
Plus if you watch the replay she is not 8 1/2 lengths behind at the stretch call. Don't get me wrong, she closed fast and ran a very nice race, but she is not the fastest horse ever.