Siobhan was a female Human and the mother of Sylvia Tilly. She lived during the mid-23rd century.
This character's name comes from the closed captioning. StarTrek.com gives Tilly as this character's surname.
It was stated that Siobhan had more than one "posting", causing her and family to move locations, suggesting she was either a Starfleet officer or a member of another service organization.
Sylvia started to say that her "mother always said...", before correcting herself: "my mother never really said anything to me unless she was criticizing my hair", when attempting to convey to Michael Burnham that she shouldn't be afraid to open the delivery of Philippa Georgiou's last will and testament. (DIS: "The Butcher's Knife Cares Not for the Lamb's Cry")
Shortly after Tilly was accepted into the Command Training Program, Siobhan spoke with Tilly via hologram. Siobhan encouraged Tilly to speak with her stepsister for input. (ST: "Runaway")
While investigating the mysterious red bursts in 2257, "subspace mom" and "return mom's last 5 messages" were both items on Tilly's to-do list. (DIS: "New Eden")
In The Way to the Stars, Siobhan is portrayed as a rising member of the Federation Security Council, divorced from Tilly's father a xenoarchaeologist in Starfleet.