The seven contrary virtues are not a fixed set, and chastity is a good place to see how loosely the scheme actually held. The list is a teaching device built by inversion: take the seven capital vices, which were themselves stabilised only gradually from the eight thoughts of Evagrius through Cassian to Gregory the Great, and name an opposite for each. Because it was built that way, it inherited every wobble in the list it was built from, and it added some of its own.
Chastity in the scheme answers lust, and it is one of the more stable entries, but the Latin behind it varies. Prudentius calls the figure Pudicitia, modesty or shame, which is a wider thing than sexual continence. Later lists give castitas. Some give sobrietas, which elsewhere answers gluttony. A preacher working from one manual and a painter working from another could easily produce different sevens.
Chastity acquired attributes in Renaissance art without ever settling on one. The lily and the unicorn belong to her, and so does the sieve, from the legend of the Vestal Tuccia who proved her innocence by carrying water in one. The sieve is the reason Elizabeth I is painted holding it.
The atlas draws no emblem for chastity for that reason. Three candidate attributes with no clear winner is a case for skipping rather than choosing, and an invented emblem would be worse than none.