The fact that you'll be back at work will make a huge difference. You'll be able to have adult conversations, you'll get time to focus on something other than "What does DD need next" and more importantly, you'll get a chance to miss your DD.
Stick any two people together for every minute of every day and they're going to start driving each other nuts. That doesn't change just because one of those people is a tiny baby. Time away from your child will make you appreciate the time you spend with her far more.
In terms of how your daughter is going to change over the next year or so, she's going to start being able to understand far more. You'll be able to communicate more, she's going to start becoming her own little person, with her own ideas and wants. I'm not going to pretend it's going to be easy, in some ways it will be much harder, but it will be different. You'll be able to reason with her, to explain that if you do this now, then later this can happen. A lot of the time she won't listen to you, but she will understand. I vastly preferred the toddler years than that first year. It was difficult, but so so much more rewarding.
Lastly, cut yourself some slack. You've had a spectacularly difficult first year with her, and you've come through it. You've lost your partner, had to learn to parent while grieving, and had to do it all by yourself.
And you've done it. Not perfectly, but then every single parent can say that. My DD is nearly an adult now, and I still have moments from that first year that sometimes pop into my head in the middle of the night, moments where I got it wrong, where I did something dangerous, or stupid.
Your child is fed, and clothed, and safe, and loved. You are winning.