Can an old widow in her iddat be in her sons nikah?

Assalam aleikum hazrat. i woukd like to know about my ammi jaan she is the widow of my father after his unfortunate death. As we have arranged my younger brother's nikah before the death of my father. Now the situation is here ammi is in iddat for 4 month 10 days and after 40 days of my father's death my younger brother's nikah date is fixed and whether our mom could get in place where nikah will going to place..(under hijaab)..please guide us.