As a feminist trinitarian theologian, I still opt to use "traditional" language for the Persons of the Trinity--Father, Son, and Holy Spirit. I make this choice because I have not found an alternative that a) preserves the integrity of the economy of salvation and b) allows me to enter into a conversation with those who do not identify as feminist or who might be coming from a more traditional background.
The decision to use the titles of Father, Son, and Holy Spirit are based on the premise that these titles are not ontological titles for God. In other words, God, in God's very nature, is not a Father or Son. Instead, these titles are relational. The Father is only the Father of the Son and the Son is only the Son of the Father. The Spirit is not independently the Spirit, but is the Spirit of.
A colleague of mine would play with language, recognizing the limitations of both language, in general, and the English language, in particular. She would say, regarding God, "Yes, She is Father." In saying this, she was skewing the perception that Fatherhood is tied to maleness, but instead that it is a relational role.
Recently, I started a new job working with residents of public housing. For the last two weeks, I have spent time with kids in public housing, many whose fathers are absent, for various reasons. This phenomenon is not specific to my particular community nor to public housing, as it is often the case in urban areas, particularly (but not solely) in African American communities. However, there are households in all demographic groups where there is no male father.
In these situations, mothers often have to assume the role of mother and father, taking on all of the parenting responsibilities. They have to do it all--as much as any one person can do it all. When fathers leave, or have never been in the picture, or are in jail--mothers step up to the plate to provide for their children, to care for their needs, to ease their fears, and more. The roles they fulfill have nothing to do with gender and everything to do with the relationship they have with their children.
Can't the same thing be said, then, about God? While our categories of knowledge and our language--particularly English--limit our comprehension of God and our ability to articulate our understanding of who God is, real life teaches us that the role of father is not solely a male role. Circumstances and contexts necessitate evolving understandings of these roles. Therefore, just as women--mothers--are fulfilling the role of fathers each day in the lives of their families, the fatherhood of God is also a fluid and relational role, not bound to an androcentric understanding of who God is. It is because of this we can say--She is Father.