The mistakes of Imlie were:
1. Not letting Adi reveal the truth at adini wedding - credits to Aparna's speech
2. Not revealing the truth to the family after adi requesting her multiple times - credits to the whole situation created by her husband
3. Not going into Adi's room after truth reveal - credits to Amma's useless advice
4. Not letting Adi know of M's behaviour - credits to her own mahaanta and babusahib ki chinta.
5. Letting SK escape - credits to her impulsivity
6. Not leaving him after he deleted the video - credits to her love for babusahib
7. Letting M stay in the house - credits to her foresight of the kid's social status
1,2 & 3 can be ignored because of the sources
4 ki vajah se eventually Adi was shot (but she did try to warn him in the beginning and he termed it as immaturity)
5 ki vajah se he started distrusting Imlie regarding SK
6 & 7 ki vajah se she became a doormat
That being said, none of these will trump his blunder of not giving Imlie the benefit of doubt regarding M and letting her stay at home against Imlie's will even as M keeps accusing her of a murder attempt.