I think I might have missed the Institute quests when I didn't agree to help her. Can I go back to the location and get it? If so where is the location? Please help as I believe I need these for PS4 achievements and 100 percent completion.
"Institutionalized" is a main story quest and cannot be skipped but in order to get the achievement you must follow the Institute quest line instead of any of the other factions.
If you choose another faction to enter the Institute during the mission The Molecular Level, you'll end up doing part of the Institutionalized questline in many instances (for example, the Railroad quests have you continue the Institute quests concurrently with their own to avoid arousing suspicion of the Institute) but you'll not complete the required mission to get the Institutionalized achievement.