Hi, sorry your sister is in this situation. I think there are links to support on the home page for this website. Usually local councils have outreach services for families of addicts, try under the carers section. My local council has one called CASH. There will be something close to her it’s just finding it that’s a bit tricky!
If you are in Lancashire it will be CASH. Google it and it will at least give you an idea of what to look for.
In the meantime your sister needs to step away from her partners chaos. She doesn’t need the stress. I’ve been in her position a few times, including with a new baby and no job. I’m still in that position but I have taken a step back. I’m glad she has you, you sound like a fab support. I’m on here everyday if you need anymore help xx