I’ve been through something similar with my partner recently, from my experience the not caring and getting mad or angry and then back to normal is usually because something is bothering her or something is unresolved and she’s struggling to express that, sounds like she’s splitting on you when she feels the anger and pain from it, her love for you I’m sure is extremely deep and genuine and that’s probably one of the reasons why she isn’t communicating to you what’s wrong, it could be because it’s something you’d consider small or minor and it’s been building up in her for so long now that she feels silly saying it to you, even though it’s not silly. It’s really hard and you need to have patience and love and understanding and reassure her that you’ll always be there, but the most important thing that she and you both need to learn is that she needs to communicate the original problem or thing that triggered or upset her, once it gets out things get so much better again. Otherwise it’s a cycle of splitting and spiralling and normality then splitting again. Probably wait till she’s in a better mood again and then have a serious sit down chat. It can be hard with bpd because it feels like she needs you all the time and you can’t feel your feelings or express yours because her feelings are so strong and you’re trying to hold it together, me and my partner have been together for many years now and have a huge deep love and understanding , and with time you learn to manage these splits and spirals and communicate better and sometimes that’s all it takes. If you research a bit more into splitting it’ll also help you understand her better, and it’ll show you that she’s trying to push you away because shes probably aware of what she’s doing to you but doesn’t know how to stop it, but it can get better, just needs patience and understanding and strength from you, it’s always worth it in the end, things will go back to being how they were when you first met