The content of this painting is particularly similar to Rokeby Venus by Diego Velazquez, with that masterpiece arriving around three decades after Rubens' contribution. The flemish painter shows the goddess with long blonde hair, in line with traditional tales, but chose to portray her in a fuller figure than other artists had done. Titian also famously created Venus with a Mirror in 1555 as well as most famously his Venus of Urbino.
Rubens was fairly consistent in his depictions of Venus, as shown in his earlier piece from 1613 - Venus, Cupid, Bacchus and Ceres. That portrait also styles her as particularly light haired and of a slim but far from skinny frame. This honest approach to capturing the female body feels more natural and gave him work integrity and a sense of realism, beyond all the fantastical themes of mythology or religion. Of course, the Baroque movement was all about energy within art and you will see the same in the paintings of Caravaggio and Rembrandt and the sculptures of Bernini.
The symbol of beauty, according to mythology, Venus appears to spot the viewer via the mirror and has a fairly neutral expression on her face. Rubens chooses a dark skinned servant as her aide in order to accentuate her own fairness. To see the great masters of the Northern Renaissance and Italian Renaissance producing their own versions of the same themes is a dream to any art historian who is looking to connect the two through stylistic and technical comparisons.