hey wehrli - I'm sorry that things are rough right now for your DP and your new family.
There are good resources and support out there for adoptive moms, for instance, who are struggling with their non gest, non bio role. They are generally encouraged to find ways to bond, there are books to read, there are groups and people who understand, they are sometimes encouraged to induce lactation, there is understanding that postpartum affects adoptive moms, etc..
In my experience this social support and understanding is not there for non-gest, non-bio moms in our situation. Where the birth mom is your DP, there is alot of social pressure to be a strong, selfless support for the birth mom and babe and their needs. There is this feeling out there - You have a baby that you 'birthed' in your family, so what is the problem? Support your DP and her needs and be patient. One day there will be more of a role for you.
That pressure certainly did NOT come from my DW. But it was a dominant social vibe for sure, one that family, friends and strangers alot said without saying. It was difficult not to feel incredibly selfish and weak to have needs.
I didn't get to a space of depression, and all parents needs are different - so I'm really just sharing this in the hopes that some might resonate or spark some ideas/conversation.
What worked for us was that we both shared what it meant to us to be a parent/mom (we both identify with mom). we looked at creative solutions to let us both be the moms we are. We always kept our lo's wellbeing at the front, but were willing to try things she might not love as much - but that were still healthy and fine options.
For instance - it was important to me to feel like I could care for our LO independantly. We used a LactAid (a bottle with tubes that you tape to your nipples) starting really early (1 week after birth). Our DD was fine with it - didn't really notice the change. I loved being able to feed her. My DW actually really loved it too. Pumping was faster than feeding. She got a little break too.
I used bottles mostly instead starting at 4 months *some women love lactaids. I loved having the option, but prefered bottles later - just easier and less stress * I was able to take care of our DD alone during the day if needed. I wasn't big on the idea of bottles before using them. I was hoping to avoid them. It is kinda hippie attachement parenting faux paux, right? but I found that attachement means both moms, and we do what we can to be the best parents we can. it is okay to do things like use bottles - especially if you snuggle and love your LO to bits while doing it :)
My DW pumped after her morning feed. She had plenty of milk then that DD didn't finish that time of day. She did this most mornings, and we just kept a supply in the freezer. We soon had way more milk than I needed, but it did all get used eventually :) This also meant that if she sent to work for a day, I already had milk, and she could store that days milk and bring it home lafter work. We didn't need to meet up. and it was less pressure, because she rarely was able to pump the same amount she would have fed our lo while working.
I remember the first time I got our DD to sleep at night alone. My DW went to a zumba class in the evening. Our DD was 9 MONTHS! I hadn't put her to sleep on my own yet because she was bfed to sleep - and it was easier and lovely. But it shocked me that night that it was the first time. That I felt so terrified I couldn't do it. Maybe it doesn't seem that shocking, but as a new mom, to feel like a mom, to feel like I couldn't do these very simple acts (feed my baby, keep her happy, get her to sleep, be alone with her for a day or many...) it just didn't feel right.
I think it is okay to explore explore new ways of doing things if it will help, even if they venture away from what you both thought you wanted for your LO a bit. Even if they are more complicated.
as long as they are healthy and reasonable.
much love and best to your fam as you struggle through this. I found blogs SUPER helpful. Like First Time, Second Time. Reading other non-bio mom's words helped me realize I'm not alone or selfish. And postpartum can totally affect non-bio moms in this situation. some caregivers might not recognize that as a possibility.