Metro: Last Light-Chapter 28:The Garden Walkthrough
As the chapter started, climb the vine to the top, and walk down ahead. Proceed toward right and shoot at the demon along some creatures on the ground attacking you. Continue down the rift and eliminate all enemies long the way.
Keep going until when you see mama (looks like a bear) for a shot period, once they have gone go toward the dead body and collect the note.
Proceed ahead and mama will start attacking you. Follow onscreen instruction to get away from her. Then move away from her and keep firing on her back (is the weak spot). Watch out for her kids, they will start attacking you as well. Keep attacking her until you kill her.
Enter the building ahead to complete the chapter.