When I looked up "lesbian" in jisho.org, I came across the six kanji term "女性同性愛者", which I'm concerned may sound too formal or clinical, like using "homosexual" as a noun in English, plus katakana words of varying lengths.
The English edition of Wiktionary doesn't have a Japanese language translation for "lesbian". Looking up weblio doesn't help much, because the entries for the English word "lesbian" mainly provide information addressing native Japanese speakers.
The accepted answer on Yahoo answers gives a couple of different answers, and doesn't seem that authoritative: https://answers.yahoo.com/question/index?qid=20070712193145AAHuB7J
I would prefer a term that's acceptable for polite, respectful but friendly conversation.