Since Emmara belongs to Selesnya guild, her usability is a tad limited in comparison to mono-color creatures. But there are two types of decks, where she will shine in full force.
The strength of Emmara in a token-based decks comes from an ability to repeatedly generate tokens. She will work great alongside cards like March of the Multitudes and Divine Visitation, which turns all 1/1 tokens into 4/4 Angels. This is undoubtedly one of the strongest combos you will witness during this Standard season.
In this case Emmara will produce tokens for the History of Benalia value. The black color is needed to get both Knight of Grace and Knight of Malice into the deck for synergy. This list should be played in an aggressive way even if it means that you will lose a token or two during the blocking step.