Advice for fixing my relationship with sister

Tldr; Sister (25) is in debt with almost 8k, only works a part time job, regularly gives shifts away to hang out with friends, has a secret boyfriend, rarely contributes to household finances and is overall not as concerned about these issues as I am.

I (21) constantly am unable to sleep, have feelings of severe anxiety and panic attacks thinking about her future. When I speak to her she always says she is worried as well but has things “under control”

Growing up my sister and I were the closest, and I still consider our relationship to be that way but this past year has been one of the worst in my life. After finishing up high-school, she went into university in a program she was interested in. Her grades were not that good, she ended up having to retake some courses, (covid also happened during her 3 year i believe which caused a lot of stress). Overall i’m not even sure if she ended up completing this 4 year program as she hasn’t signed up for graduation or anything. She ended up going to a different college after this with a new program she said she was more interested in. Due to her grades she wasn’t able to receive any financial assistance from the school, and she put this onto a credit card, thinking she’d be able to pay it off (very very stupid idea). She was able to complete a semester, but could not apply for the next term as she couldn’t cover the cost anymore. (This new sem was beginning in jan/25) I had a serious talk with her and told her she needed to get things straight – work more hours at her job (since she wouldn’t be in school anymore, she had all this free time) , or get a second job – anything to get more income and cover these costs. I should also mention that we are a low income family, growing up we only had a single mom that really tries her best for us and wants us to succeed which is why I’m constantly so sad and anxious about this because she has no idea about the debt and lies. It’s now august, and she hasn’t managed to pay off a single cent, or save anything, in fact there was a period where she was actually buying clothes, and unnecessary things but this has stopped now as I think she doesn’t have anything else to spend. I’m constantly wondering, how is this possible? She doesn’t pay rent, will sometimes cover groceries (200/ month), or other little things. She has a boyfriend that my mom doesn’t know about, and i only know because she’s constantly on the phone with her “friend” and the way she talks to him is certainly overly friendly… It hurts me that she didn’t trust me enough to tell me about this, and lies and gives away her shifts so she can go hang out with this guy and her other friends. She has lied to my face by saying that her manager “cancels” her shifts but i’ve over heard her calling out. , or saying she’s at work but her location has showed her at restaurants, movies, parks etc, Recently, my mom has been more tough on her to contribute to the household (paying the phone bill, or rent or groceries) there have been times where she’s asked me for money and i’ve covered the costs without telling my mom i’m the one that paid My mom will get mad when she’s out with her friends and constantly goes on these rage filled rants telling me about how she (sister) needs to grow up, do better, be more responsible but by the time my sister gets back home, my mom has fallen asleep and just forgets to lecture her leaving me to be the one to do it, and the cycle repeats. There’s been times where my mom has expressed that she wants to die because of how my sister acts, how she feels like a failure, it gives me so much anxiety and sadness hearing this, but as soon as my sister does something “good” (pay for groceries, or clean the house) suddenly she forgets about it until it happens again. i’m only 21, i shouldn’t be crying myself to sleep every night because i’m worried my sister is gonna end up homeless, but the lies and just her overall attitude to this situation is eating me alive.

I don’t know how to talk to her about this anymore, every time i do i just end up crying and she apologizes for making me feel so stressed but we’ve talked about this issue at least 4+ times and nothing has changed. I don’t know if i should mention that i know she has a secret bf and hangs out with him instead of going to work (leaving me to have to contribute more financially to the household and her)

I love her so much but just wish she would be responsible. I’m scared of our relationship being ruined over something as stupid as finances and lies.