A holoscreen is a portable, digital computer monitor that is used for the purpose of sending reports back to the Galactic Federation during a mission.
SPC M. Angseth complains in her final Log about being confined to staring at a holoscreen during the Splinter infestation, despite believing she could outshoot her fellow soldiers in the GFMC Task Force Herakles. Angseth's body is found in the Trooper Security Station, which does not feature any computer screens that could be definitively identified as the holoscreen she mentioned. It is possible that she was referring to computer monitors found in previous rooms such as Hive Chamber A and Command Chamber, which can be seen displaying images of Federation Marines and converted cargo pod gates by the time Samus Aran enters the Splinter Hive. This would suggest that Angseth was not in the Trooper Security Station when she recorded her final Log.
SPC M. Angseth
This is ridiculous. I can outshoot half the men here, and I'm stuck on monitor duty. I didn't join up to stare at a holoscreen! This wouldn't happen to Samus Aran... She'd be out there taking care of business, not pushing buttons and sending reports.