Plot hole: "Red" is somehow serving a life term or what for the execution murders of some Russian spies, her husband and his cronies had headed up. But her hubby somehow escaped any such sentencing.
Continuity mistake: During episode 6-3, it is established that all inmates at the Ohio prison facility are required to have their hair cut in order to prevent the spreading of lice. Later on in the series, it is revealed that almost all of the inmates that were not moved to Litchfield Max after the riot were sent to Ohio. Despite that, several of the inmates formerly from Litchfield were shown still having long hair in scenes that took place in the Ohio facility, and Maritza's hair was long when she first appeared at the nightclub while she was on parole. While it is possible that the policy may have been rescinded between the events of seasons six and seven (which would explain why Alex's hair was still long when Piper visited her), that does not explain the other characters that were immediately transferred to Ohio still having their hair long during subsequent appearances.
Continuity mistake: When Piper confronts Alex in the bathroom (saying "you named me"), When Alex turns away you can see that her salt shaker tattoo is upside down.
Continuity mistake: Near the beginning, Piper is sitting on the toilet and you can see her new engagement ring on her finger. When she wipes her eyes with the tissues the ring has vanished. A couple of shots later the ring is back.
Continuity mistake: As 5 women are walking through the park several extras can be seen in the background. Camera angle switches to aerial view, and the 5 women are the only ones in the park. (00:27:05)
Lesbian Request Denied - S1-E3
Continuity mistake: Larry and Cal are cooking hot dogs over an open fire. Larry starts out with a straight stick, Cal with a curved stick. Larry puts his hotdog on the curved stick, then has the straight stick as he puts it over the fire. The swap happens again and Larry ends the scene with the curved stick. Also, the tip of the straight stick swaps from a sharp point to a dull point. (00:40:30 - 00:41:50)
Blood Donut - S1-E7
Continuity mistake: When the girl is holding the flash light to her face, the next shot it's the other way around, then a couple of seconds later it's the first way again. (00:14:40)
Blood Donut - S1-E7
Visible crew/equipment: When Flores discovers her cell phone is missing from the hole in the wall she goes nuts, slams the stall door and kicks it in. After she is taken away there's a closeup of the stall and we can see the metal spring that was duct-taped to the bottom of the wall inside.
Moscow Mule - S1-E8
Continuity mistake: Mercy, who was released several episodes earlier, can be seen sitting at the table when Maria comes back in.
Factual error: Whenever Tiffany gets her dentures there's one problem. She's got her hands cuffed in front and prisoners, unless they're cuffed to the waist and ankles too, should have her hands cuffed behind her back.
Take a Break from Your Values - S2-E11
Continuity mistake: When Piper calls Alex she is drinking wine till the glass is empty but in the next shot the glass refills by itself.
Continuity mistake: When Angie tries to smuggle cake out of the cafeteria, she puts away her tray and then tries to slip after the guard. When he stops her, she turns to make her way back to the now empty table; in the next shot, the tray is on the table once again. (00:16:25)
Continuity mistake: We see Sophia's long hair from the side as we watch Red and Mendoza talking. A minute later, we turn back to see her face and she has a short shoulder length haircut. (00:48:10)
Continuity mistake: In season 3 Baxter Bayley's uniform reads C. Bayley. In season 4 it reads B. Bayley.
Character mistake: At the end of the episode when Maria is framed for the prison panty business and told to expect an additional 3-5 years on her sentence she cries saying that her daughter Pepa will be in kindergarten by the time she gets out. However in season 2 episode 12 Maria tells Piper that she still has 6 years left on her sentence. This means that even without the extended sentence her baby would have been well past kindergarten age by the time she was released, so taking the extra 3-5 years into account, Pepa could be almost finished in elementary school by the time her mother got out of prison.
Factual error: Tiffany asks a guard where he would go if he could travel back in time. He says he would return to 1999 to attend a Judas Priest concert he missed. He says he wasn't able to get close to Rob Halford. The problem is Rob Halford was not the lead singer of Judas Priest in 1999. Tim 'Ripper' Owens was.
Full Bush, Half Snickers - S5-E7
Continuity mistake: When Red and Flores are texting Piscatella to come into the prison from Humps' phone, in one of the texts, Humps says "Thx" and Piscatella texts "Np". The time Red and Flores send is 4:59 and the text is sent from iMessage. When Piscatella checks his phone the time is 4:56, the messages were sent by the opposite people, and it's an Android phone, incompatible with iMessage. (00:53:03)
Character mistake: The zip tie handcuffs on the arrested inmates were not tightened. (00:25:18)
Character mistake: The officers count the inmates and say there's 10 missing. There are indeed 10 inmates hiding in the pool. However, Pennsatucky and Chang had escaped the prison. The officers counted Linda as an inmate, who had been hiding in Litchfield the whole season, and wasn't on the list. That would make it 11 people missing, not 10.
Continuity mistake: In season 5, CO McCullough mentions that her first name is Artesian. However, in season 6 her uniform says her name is B. McCullough.
Answer: You would need to be more specific as to which inmate to get an answer as to who possibly belongs in the mental ward. In general; usually the only mentally ill prisoners who go to the mental ward are inmates who show obvious psychotic breaks like Loli and crazy eyes as, with the conditions of prison, it's often difficult to tell who is mentally ill and whose frustrated from the conditions. Many of them are also only there temporarily. Crazy Eyes, first example, was in the mental ward. Her mother fought and won to get her out.