Mother's Day

An unknown woman enters a maternity ward and, with help from an accomplice, steals a newborn baby. Beth Sohapi (Jaime King) is having a birthday party for her husband, Daniel Sohapi (Frank Grillo) with the help of their friends, married couple Treshawn (Lyriq Bent) and Gina Jackson (Kandyse McClure); Dave Lowe (Tony Nappo) and his fiancee, Annette Langston (Briana Evigan); George Barnum (Shawn Ashmore) and his girlfriend, Melissa McGuire (Jessie Rusu); and Daniel's co worker, and friend, Julie Ross (Lisa Marcos). The news reports a tornado is heading their way; Daniel assures his guests that the basement is tornado proof.
After a bank robbery gone wrong, three brothers, eldest and leader Ike (Patrick Flueger), irrational and irresponsible Addley (Warren Kole) and Johnny (Matt O'Leary), who has been badly injured, are on the run from the law. They reach their mother's house only to find it unrecognizable. Daniel and Beth, hearing noise upstairs, leave the basement party only to find the brothers holding them hostage within their home at gunpoint. Terrified, Beth offers the brothers the help of George, a doctor, who begins to tend to Johnny's injuries. Addley forces Beth and Daniel downstairs, trapping all the party-goers in the basement at gunpoint. Ike calls his sister Lydia (Deborah Ann Woll), who informs him that she and their mother lost the house and will be on their way to help the boys.
A short time later, an RV arrives with Lydia and Mother (Rebecca De Mornay). Mother becomes very angry at Ike for losing the emergency phone they use to contact one another, telling him she was unable to alert him of losing the house. Realizing the gravity of the situation, Mother arranges help to sneak over the border into Canada, however it will cost ten thousand dollars. She learns of her sons sending money to the house which she never received, before going into the basement. Mother is initially nice to the hostages, explaining to them that no one has to get hurt. She confronts Beth and Daniel about the money, however both deny knowing about it. Mother believes Beth, however she has Addley and Ike torture Daniel for information. Just then Melissa attempts to escape, only to be shot by Addley. Mother takes the cellphones, bank cards and pin numbers of the others and makes Ike take Beth to a cash machine to collect the money. Meanwhile, Mother informs George to keep Johnny alive, or they will all die.
A police officer (Mike O'Brien) arrives after the three suspects of the bank robbery are identified as the old residents of the house. Daniel assures the officer everything is fine and he leaves, alerting Mother of Daniel's lying skills. She further becomes suspicious after Lydia discovers a Valentine's card from Daniel to Julie, as well as photographs and newspaper articles of a child killed in a car accident. Ike and Beth dispose of Melissa's body behind a dumpster, where she is soon found to be alive by two sanitation workers who rush her to hospital. While at the ATM, Beth and Ike encounter two party girls, Vicky Rice (A. J. Cook) and Jenna Luther (Alexa Vega), who Ike quickly kills after they realize he has a gun. The pair travel to Treshawn's laundromat business to take money out of the safe, where Beth attempts to escape but fails. They later encounter the police officer who Ike also kills. Back at the house, George realizes Mother has been lying to Lydia about a rare skin condition and tries to convince her to help his friends, but Mother sends Lydia away. Johnny, now in critical condition, tells his mother he doesn't want to die a virgin. Mother forces Treshawn and Dave to fight over which one of their partners will be forced to have sex with Johnny. Dave loses and Annette is forced upstairs. However Johnny's injuries prove too severe to rape Annette and she is forced back into the basement by Addley. Dave attacks Addley, resulting in Addley shooting Dave in the face, killing him. Gina takes the opportunity to try and escape, however is brought back to the house by Daniel in order to save Beth.
In the basement, Mother informs Gina that disobedience has consequences, before pouring boiling water over Treshawn. Mother then attempts to find her money by burning the photographs of the boy, revealed to be Daniel and Beth's deceased son. Mother then sets Julie's hair on fire, but extinguishes it when she realizes Daniel is telling the truth about the money. Mother leaves the basement, before the group manage to arm themselves with knives. They lure Addley into the basement and stab him to death. Treshawn, now deaf and having difficulty seeing, takes Addley's gun and goes upstairs. Gina follows him, startling him and causing him to shoot her in the side. As Treshawn attempts to help his wife, Mother shoots him in the back, killing him. Mother discovers Addley's body and phones Ike, before forcing Beth to listen to her shoot Daniel. Annette and Julie are then taken upstairs and tied up.
At the hospital, Melissa regains consciousness and alerts authorities to the house. George confronts Mother, telling her that none of her kids look like one another, and look nothing like her. Mother, enraged, threatens to kill him, but Lydia convinces her that they need George. Ike and Beth then burst through the front door with the money. Mother instructs Ike, Lydia and George to take Johnny to the RV while she has a chat with the ladies. Inside the RV, Johnny shoots George in spite of Lydia's pleas to let him live. Mother reveals to Julie and Annette that Beth was the one who hid the money and is the one responsible for all the deaths. Beth reveals that she was hiding the money for the baby she is expecting. She also reveals she knew Daniel was cheating on her with Julie, and wanted to leave him. Mother forces Beth to take a pregnancy test to prove it, before Beth knocks Mother unconscious. Beth unties Julie, who is shot in the head by Ike while trying to escape the house, and Annette, who hides with Beth in the garage. Together they manage to overpower Ike and kill him. Annette escapes to the neighbours, while Beth fights with Mother in the house. Beth is knocked unconscious and Mother sets the house on fire. However, Beth wakes up and overpowers Mother, hitting her with a wooden chopping board, before escaping the house along with Gina who has survived her injuries.
Months later, a very pregnant Beth goes into labor and is taken to the hospital by Annette, Gina and Melissa. That night, Beth wakes up to the emergency alarms going off in the maternity ward. She gets up and goes to check on her baby, but the bassinette is empty. The film ends with Lydia, Johnny and Mother leaving the country in the RV with Beth's baby.

Question: Why does the Mother want to kill George?