Is it forbidden to speak to and ask about a non-Muslim female friend who practices lesbianism, knowing that previous conversations with her were about life matters and cultural differences?

Acquaintance, conversation, and correspondence between a man and a woman who are not mahram (definition), without a valid need, is a gateway to fitna (temptation/strife) and corruption. Claims of friendship, collegiality, or that the relationship is within the bounds of decorum are all contrary to Islamic law (Shari'a) and have unreliable outcomes, as fitna is not safe when there is no valid need. Jurists have explicitly stated the prohibition of speaking with a non-mahram woman without a need. Al-Khadimi said: "Speaking with a young woman who is not a mahram is impermissible without a need, because it is a place of fitna." If these relationships are forbidden, they are even more strictly forbidden with corrupt women.