Cynthia observed a cell with a pair of sister chromatids moving toward a giving pole as a single unit and another cell with sister chromatids moving to opposite poles. what did she infer from her observation?

The answer is The first cell is in the anaphase I and the second cell is in the anaphase II.

Meiosis is a cell division which results in the reduction of chromosome number by half - from diploid to haploid - in daughter cells. It consists of meiosis I and meiosis II. Meiosis I produces two haploid cells. Meiosis II is analogous to mitosis, so in total, meiosis results in four haploid cells. So, in meiosis there are two anaphases - the anaphase I in meiosis I and the anaphase II in meisosis II.
In anaphase I, the sister chromatids separate from each other to the opposite sides of the cells. In meiosis I there are 46 chromosomes in duplicate, which are present as pairs of sister chromatids. In anaphase of meiosis II, since the cell is haploid, there are 23 chromosomes in duplicate, which are present as sister chromatids.