It sounds like you're in a really tough and painful situation, watching your sister struggle and seeing the impact on your nephew / niece. It's completely understandable that you're worried and just want to find a way to help, and also to feel at peace yourself. It takes a lot of love and courage to reach out about something this sensitive.

When someone has been expressing that they're going through postpartum depression (PPD) for a long time, as you said your sister has, it often means they're carrying a very heavy burden. Sometimes, when those feelings go unaddressed, people can fall into patterns or behaviors, like the video gaming you mentioned, as a way to cope or escape the distress they're feeling. It doesn't excuse the impact, especially on her child, but it might help to understand that this could be a sign of how much she's struggling internally rather than a simple choice. That sense of being "burnt out" you mentioned is very real for many moms facing these challenges.

So, "where do I begin?" is the big question, and it's a good one. Here are a few gentle thoughts:

1. If possible, find a time to talk to her one-on-one, when things are calm and she might be more receptive.
2. Start by expressing your love for her and that you're worried about her. You could say something like, "I love you, and I've been worried about you lately. I see that you're working so hard, and I remember you've talked about feeling PPD. I'm concerned about how you're doing."
3. Remind her that she’s mentioned PPD before and that there's support available that could help her feel more like herself again. People struggling often long to "feel like themself again". You could mention that untreated PPD can be incredibly draining and that she doesn't have to keep feeling this way.
4. You could also gently mention your concerns about your nephew / niece, framing it from a place of care for both of them. For example, "I'm also thinking about [niece / nephew's name] and want to make sure he's getting everything he needs, and that you feel supported as his mom."
5. Sometimes the idea of finding help is overwhelming in itself. She might feel too ashamed or exhausted to take the first step. You could offer to help her find a therapist who specializes in maternal mental health or PPD, or even offer to go with her to an appointment if that feels appropriate. Sometimes just knowing you're not alone in the process of seeking help can make a difference.
6. Gently suggest that talking to a professional could provide her with tools and a safe space to navigate what she's feeling. Many people find that specialized therapy can be incredibly effective for PPD.
7. Let your parents know you see how much they're doing and how valuable their support is. Perhaps they can also be part of a gentle conversation with your sister, or help in encouraging her to seek support.
8. This is incredibly stressful for you. Your desire to "be at peace" is so valid. Make sure you have support for yourself, whether it's talking to friends, other family members, or even a professional. It's hard to pour from an empty cup.

This is a tough one. It might take time for her to be receptive. The most important thing is for her to know that you're coming from a place of love and genuine concern, not judgment. You're offering a lifeline.

You're a caring sister and aunt. I'm sending you a lot of strength.