Of course she can. You are legitimite persons according to this
Emirates My Family
You can invite any members of your immediate family to join. If they’re not already Emirates Skywards members, they’ll just need to register first before you can add them. Immediate family members include the following: Husband, Wife, Domestic Partner, Son, Step‑Son, Daughter, Step‑Daughter, Mother, Mother‑in‑Law, Step‑Mother, Father, Father‑in‑Law, Step‑Father, Brother, Sister, Granddaughter, Grandson and Domestic Helper.