All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.
If a man creates an account in the name of a woman, then there is no doubt that this is not true and it is really a lie. Lying is forbidden except for a necessity or dire need which one does not achieve except by lying. Nonetheless, it is acceptable to use a nickname which is used for both males and females, such as the names Ihsaan, Amal, Badr and the like. This is a kind of use of equivocation or double meanings when the need arises; for more benefit, please refer to Fataawa 84728 and 88412. However, if the group is restricted to female members, then a man should not resort to trickery to join it.
Even though we said that it is permissible to use a nickname that is used by both males and females, it is still more appropriate to avoid this in principle and leave the matter of calling women to women as a man might fall into temptation. Also, he might need to use the feminine pronouns for himself when he is addressing them while he is a man, so it is better for a man to avoid this and to dedicate his efforts to addressing men; and being safe in regard to your religion is of unrivaled value.