Mahabat Khan took Jehangir/Shariyar/Dara Sikoh/Aurangzeb hostage in lahore where he was camping but to entire world he showed as if Jehangir is still comanding him. This was in 1626.
But Nur Jahan escaped and joined her daughter ladli and her grand daughter on other side of river. Then Nur Jahan commanded a mughal force to rescue Jehangir/Shariyar etc
The attack failed and hence Nur Jahan surrendered with her daughter/grand daughter to Mahabat Khan
When Shah Jahan heard all this he decided to rescue his father and kids and proceeded to Lahore from deccan. But before he reached Jehangir’s camp Nur Jahan had already rescued him using her brain. Nur Jahan ordered him to return to deccan.
Then she told Jehangir to take Mahabat Khan into confidence and tell him everything Nur Jahan was planning. Jehangir did that and Mahabat Khan started trusting Jehangir. The emperor’s camp shifted to Kabul. There Jehangir tricked the forces and Mahabat Khan forces were seperated from him. The royal body gaurds of Jehangir surrounded and killed/sold many of Mahabat’s Khan forces. Some of his loyalist had already joined Jehangir camp. Mahabat Khan fled to join Shah Jahan.
Nur Jahan may not have given him heir she married him late at 35 past age when women gave birth in those times. So i am sure Jehangir did not marry her for heir/children he just loved her as a childhood friend and love. Secondly although she did not give him heir she and Shah Jahan were defacto rulers on his behalf for decade from 1615 to 1620 when Khurram rebelled. Although Jehangir was emperor Shah Jahan handled warfare and outside affairs and Nur Jahan handled internal matters for a decade on Jehangir behalf.
Why could Jehangir not handle empire on own- he handled but he was not wordly wise and street smart like his son Shah Jahan or manipulative like Nur Jahan to understand others. Also he was unwell by wine addiction liver problem and heart problems and asthama etc so many ailments its great he survived till 58 years. So Shah Jahan and Nur Jahan helped him handle everything after 1615.