I guess Alpha must have sensed that Nelia could see or detect her? How would even that work? Even if Nelia is able to receive old domain signals, would she be able to intercept or process those from Alpha? I thought Alpha had restricted her visibility to only permit Akira to see her, but perhaps not. Others have seen her before so it's plausible that she either can't control it or her signal was intercepted by Nelias device.