Is female homosexuality against the Law of Moses? While there are a few passages in the Old Testament that are taken to condemn male homosexuality (e.g. Lev 18:22, 20:13), I am not aware of any that condemn female homosexuality. It seems to me that all the Biblical arguments against female homosexuality must either rely on:


a single NT passage, Romans 1:26-27 (is an NT passage good evidence for what the law of Moses says? - assuming this passage even is about female homosexuality), or
more indirect arguments (e.g. Adam and Eve as an ideal that all human beings are required to conform) - the very indirectness of these arguments supports doubting them
Traditional Judaism considers female homosexuality to be prohibited, but there is disagreement about whether this is a biblical or post-biblical prohibition (and if the prohibition is post-biblical, then it has little value for those outside of rabbinical Judaism)


So is it fair to say that female homosexuality is not prohibited by the Law of Moses?
Quite simply, no, it's not fair to say that.  I do not know Hebrews, but I do know that in Greek, the word anthropos indicates a generic man or person, while aner means specifically a person who is male.  If we went through the entire Bible and applied an exclusive gender wherever it said "man", it would be nonsensical.


  Whoever sheds the blood of man, by man shall his blood be shed, for
  God made man in his own image.  Genesis 9:6 ESV


So, capital punishment if anyone kills a man, but no punishment for killing a woman?


  Thus says the Lord: “Let not the wise man boast in his wisdom, let not
  the mighty man boast in his might, let not the rich man boast in his
  riches, 24 but let him who boasts boast in this, that he understands
  and knows me, that I am the Lord who practices steadfast love,
  justice, and righteousness in the earth. For in these things I
  delight, declares the Lord.”  Jeremiah 9:23-24 ESV


So, men should not boast about wealth or wisdom or strength, but women can?


  I know, O Lord, that the way of man is not in himself,
  that it is not in man who walks to direct his steps.  Jeremiah 10:23 ESV


And a man's life is not his own, but woman's life is?

So, again, no, we cannot exclude female homosexuality as being lawful under Mosaic Law just because the word "man" is employed.  At best, it would be an argument from silence, but it really isn't from silence.