The woman is a little reluctant to give the exact details, but she eventually tells you exactly where you need to go. Apparently the gang has taken up in some forgotten section of the Undergrowth's sewer section. Finding it would normally be difficult, but her directions should allow you to navigate the tunnels with ease.
She also informs you that while you've dismantled most of the gang over the past couple days, there should still be a couple left. Bruno will not be alone.