One hundred percent, it's not possible to reach values like this only staying 15 days in altitude. So high level of Hematocryt is almost common in people living on the Ande Mountains (between 3000 and 4000m, over than 12,000 feet), but for example is very far from the values of Africans in their highlands.
So, there are two possibilities only :
a) The athlete took some drug for enhancing her values
b) There is some problem in the machine (sometimes it happens)
However, these values can't give a real picture of the situation, without knowing other parameters.
For example, the volume of the Red Cells and their number (their product gives the hematocryt, that is a number).
In any case, haemoglobin at 21,1 is something crazy, and very, very dangerous for the life of the woman. And, between me and you, completely useless for running faster.
The blood of that lady is mud, with very high viscosity and consequent big problem in the body circulation.
During the next week-end, I will be in Colorado Springs for a summit of middle distance. In that occasion, I want to show the data of several athletes running, I think, very much faster than the lady you refer. Their hematocryt was about 37, their haemoglobin under 12.
Gelindo Bordin, that is a man (men have normally 2-3 points of haemoglobin higher than women), won the Marathon in Olympic Games 1988 with 12.8 of haemoglobin, in spite of all people thinking that only with very high values of hematocryt is possible running fast.