I think my sister needs help but my parents are being selfish - Help!

This is a long story but I’m going to try to shorten it. I’m 18. My parents are always broke because my mom doesn’t work and my dad binge drinks & smokes daily. We once had a CPS case but she ghosted on us a year ago. I use to go to counseling and had severe depression to the point my dad and I had the same prescription at 10 years old, but my parents cut it off after a month because of costs. I’ve always noticed that my sister (14) has had anger issues. My boyfriend of 2 years has bipolar and went without his meds for a week bc of costs a couple months ago. In that week, I noticed that my sister acts EXACTLY how my he does when he has no meds. I brought this up to my mom as soon as I noticed it and she asked my boyfriend about it but never mentioned it after.

The past few days, I feel like she’s getting worse. The other day, she challenged to fight me & became aggressive with me when I asked her not to push the dog. Yesterday, she made a weird comment about death. Today, she sat upstairs bawling her eyes out for 3 hours about her relationship with my dad. When I checked on her, she told me how she cries herself to sleep every night over it, how much she missed our “old family”, how she feels heartbroken & angry, and how she made a fake facebook to look at old pictures when we were all happy.

I’ve offered to get her help multiple times but my mom doesn’t want her to because she thinks they would make another CPS report and get another case. What should I do?