What I found crucial to my being at home full time for 7 years (until my son was 7, he's 12) - a huge role change for me -I'd worked at an intense career for 15 years prior to that, we were newlyweds and I hadn't been unemployed in close to 20 years - and we relocated to another city -was trying to keep communication going - because you can think you have the basics down but then there's a curveball (our son is 12 so he's not a baby but covid sure was a curveball) - we had curveballs like my in-laws being ill in another city, etc. My husband's older cousin told me early on (she was home with her 3 kids for many years) that it's crucial not to let resentment grow if you feel you're doing too much.
You're doing your part totally -IMO - but with resentment. That can become poisonous to a relationship. My husband sleeps in every morning and is a night owl -he gets tons of work done at night. I really resented this in particular this year because our son was all virtual at school and now I do work part time and was teleworking. So I was "on duty" for over two hours every morning and had to keep son quiet in our small home.
It came to a head for me when I injured my foot because I was running to the other room to keep our son quiet while husband slept. That was my moment . I told my husband -I'm not running anymore to do that. I will do my best which doesn't include risking injury. And what I do is that after 9am I am off duty -meaning if son is loud, oh well. I don't do anything loud intentionally but my role in keeping him quiet which is stressful at times is -- finito.
So deal with any resentment ASAP and in a mature, calm way -and I'd be really basic about it - what can she do differently - on a practical level -that would help you feel like things are more fair. I'm not into keeping score or 50/50 -each couple decides what is fair. If you're feeling upset/resentful then it's probably not fair and needs recallibrating.
Good luck! (I also agree she might not be feeling well/depressed). I'm sorry you're struggling.