The Empress is a passive, wise, nurturing, supportive energy, associated with the natural world, abundance and fertility. She is the Mother archetype of Tarot. The Queen of Pentacles represents a practical, down to earth person, who's focused on everyday matters, financial stability and material security. The Queen of Pentacles often represents a person of an earth sign/ascendant (Virgo, Capricorn, Taurus). The Empress and Queen of Pentacles combination shows preoccupation with practical matters or matters of the heart.
To understand the elemental relationships between the cards, we should always take into account their actual meaning. The elements of the cards are Earth (Empress) and Earth(Queen of Pentacles). A very strong combination that can display slow, but steady results or if ill-aspected, a rigid, stubborn approach/attitude.