Longarekel:acharei eineichem refers to looking at anything that could lead to any form of ‘prohibited relationships’ and this definitely applies to women as well.
What you refer to as “prohibited relationships” in my mind, is someone who has a relationship with an Erva. A woman with a woman is not an erva if I am not mistaken. If the whole issur of women being together is because we shouldn’t act like the mitzrim, then the avierah isn’t an erva issur, rather a “bechukosehem lo telechu” type of avierah.
Therefore the hirhur or looking at of another woman should not be an issur in itself. Hirhur avierah is not an aveirah unless the torah points it out.