If it is a separate place and it is not part of the masjid, this is permissible.

But if is part of the masjid and that they use it to pray in it on Fridays or Eids, this is not permissible.

I heard on umdatul ahkaam you saying that women can’t enter masjid in menses. I live in New Jersey. I volunteer on every Sunday to teach children about Islamic teachings. In our masjid we teach the children in basement were we don’t perform salah only we give the classes so is it ok for me to go there only in basement to teach the children wheni have menses