Actually, if you read the Old Covenant law carefully, only bestiality and male-on-male anal sodomy (among sexual sins) are listed as abhominations.
Both medieval Anglo-Saxon and Greek penitentials penanced lesbian erotic behavior either as mastrubation or as fornication—as sin, but not as sin-unto-death. (Orthodox usage makes a distinction between those sins for which were punished by execution under the Old Covenant, setting the canonical penance as excommunication with communion on the deathbed only, termed sins-unto-death, and other sins.)
The Old Covenant law did not directly address lesbianism, though logically it would be just as much of an abomination as homosexuality among males. Paul, however, in Romans Chapter 1 clearly states the evil of lesbianism and attributes the practice to those particularly degenerate cultures.