Is there any evidence in the Old Testament that God can be considered feminine as well as masculine? I would say there is, although we have to look a little below the surface for it.
The Old Testament has if anything an even more patriarchal atmosphere than the New, but even in these earlier Scriptures, there are hints of the nurturing, mothering nature of God. In Deuteronomy, Moses compares God to a mother eagle watching over her young. While most modern English translations use the neuter ("its nest", etc.) in this passage, the original Hebrew is feminine. Here it is from the KJV:
As an eagle stirreth up her nest, fluttereth over her young,
spreadeth abroad her wings, taketh them, beareth them on her wings:
So the Lord alone did lead him, and there was no strange god with him. (Deuteronomy 32:10-12)
Much later in Jewish history, the final chapter of Isaiah uses explicitly feminine and mothering imagery to describe the return of the exiled Hebrews to Jerusalem, culminating in this declaration from God:
As one whom his mother comforts,
so will I comfort you;
you shall be comforted in Jerusalem. (Isaiah 66:13)
A particular word used many times throughout the Hebrew Scriptures to refer to God’s nature is
racham, meaning compassion or mercy. It is even used specifically as a name for God in Deuteronomy 4:31 —
El Rachum, "God of Compassion". This term derives directly from the Hebrew root word meaning "womb" — a very clear reference to God’s love as the love of a mother for her child.
One of the earliest names for God given in the Bible is
El Shaddai, dating from the time of the patriarchs onwards. There's no absolute agreement among scholars on what this name originally meant; most English translators render it as "God Almighty", on the basis that
Shaddai may come from the verb
shadad, "to overpower or destroy". However, other Hebrew scholars have suggested that it could be derived from
shad, the Hebrew word for "breast", and may also be connected with
dai, meaning "sufficient" or "enough" — implying the nourishing, sustaining, all-sufficient nature of God’s goodness, nurturing as a mother nurtures her child.
(More information on this topic here:
The Hebrew Names for God - El — scroll down to "The All-Sufficient God".)
One hint of this feminine, mothering aspect of
El Shaddai, even very early in OT times, is seen in Jacob’s blessing on Joseph in Genesis 49:25:
by the God of your father, who will help you,
by the Almighty [Shaddai]
who will bless you
with blessings of heaven above,
blessings of the deep that lies beneath,
blessings of the breasts [shadaim]
and of the womb [racham].
So as I see it, there is definitely a legitimate basis for concluding that God is equally our Father and Mother — regardless of which pronouns we choose to use for God, if any.