In the Roman Missal for the Ordinary Form there are two versions of the prayer beginning “I confess”.
In the section “The Order of Mass With the Participation of a Single Minister” it has:
“I confess to almighty God
and to you, my brother, …
therefore I ask blessed Mary ever-Virgin,
all the Angels and Saints,
and you, my brother,
to pray for me to the Lord our God.”
In the section “The Order of Mass” it has:
“I confess to almighty God,
and to you, my brothers and sisters, …
therefore I ask blessed Mary ever-Virgin,
all the Angels and Saints,
and you, my brothers and sisters,
to pray for me to the Lord our God.”
Different words depending on who you are praying with. If the minister were female it would make sense to say “and you, my sister”.
If the Mass were being said by the Priest on his own it seems to me it would be better to use another of the options for the Penitential Act, for example “You were sent to heal the contrite of heart, Lord have mercy. …”.
[Excerpts from the English translation of the Roman Missal © 2010 International Commission on English in the Liturgy Corporation. All rights reserved.]