Anna Pavlova and Vaslav Nijinsky were also famous dancers during this period.
In Opera, the Prima Dona is the singer of the principal female role, so perhaps it the leading lady in the ballet? I've never heard the term applied to ballet before. I'd imagine though it's either prima ballerina or prima ballerina assoluta status.
I don't know for sure, but I'd imagine that status is based on talent and seniority, but mostly on talent. Mathilde Kschessinka was one of only two prima ballerina assolutas in the world, so I'd imagine getting to the top was extremely difficult if you were not skilled enough.
