as i said the only reason behind is the sanitation (as far as i understand, if there is any other reason then let us know)....as u know when women have period and esp in the earlier condition, when there was not proper way of managing it...with only cloths.......it was not good to let them participate in last or other ritual process...but with the development of different sanitation products...its definitely not worthy to deprive them from any ritual process..(if you want to continue with that ritual process)