I had a feeling this might happen.
That fast 800 killed her legs, especially the first lap of it.
Yeah. Something I noticed when watching that was that she seemed to be "leading with her feet" a bit on that first lap, rather than leading with the knee. Of course, if you're running fast enough your center of gravity will still be almost directly above, when the foot contacts the track; but if you slow down some, the foot will tend to land well ahead of the COG and be a braking force.
On the other hand,
a) on the second lap it seemed like she was actually bending the knee and landing the foot pretty well under the COG, so no big braking forces; and
b) the coaching she gets is some of the best in the country; probably is aware of all that I spouted above; and may well have a better idea (than I do) about how this particular athlete runs best. Of course, a 2:03r does tend to validate that...