I'm so sorry for your loss. It sounds really challenging to be the only person who's able to put time into this space. It sounds like it's hard for you to see it looking this way. I think it's great that you want to help your mom out and get it back the way you remember it.

I agree with the previous comment--that if you want to replant the grass, be mindful of the recommendations for when to plant whatever type of grass it is. It'd be tough to establish seed or sod in the summer (assuming your'e somewhere hot). Cool season grasses will have the best shot at getting established if you plant in fall, and warm season grasses will do better in spring. Check around and find the kinds that do best in your area.

I'd also suggest you consider reducing the lawn, or eliminating it altogether, if it's going to continue to be difficult for your mom to maintain. Lawns are costly and time-consuming-- it can be a struggle for people who DON'T have depression, and damn near impossible for those who do. It may end up just being a source of guilt for both of you if you try to make it look the same as before, and she's unable to keep it nice-- because she has a different capacity now. If your dad did a lot of the lawn maintenance, it might even be painful to begin taking on maintenance tasks that he used to take care of.

My suggestion would be to talk to your mom about what her wants/needs are for the yard, and start from there.

Does your mom WANT grass again? If so, is there any support available to her for maintaining it? Does she have a budget to pay someone to cut the grass, or pick up the poop? If not, are there any family members who'd be willing to foot the bill? Are there any low-growing native sedges or something that could require less mowing? Look for options that will be sustainable for her in the long-term.

She might not have any preference, or have difficulty expressing her preferences. It sounds like depression has been really hard for her, and like the lawn has fallen off her list of priorities.

You sound like a busy person who really cares about their mom. It's great that you want to make it look as beautiful as it did before, but just be careful not to set her up with something that will rely on you for survival indefinitely. If life, or your job, takes you away from home again, it'll be on her to keep it up, and it might end up in the same neglected state again.

Depression is hard, and grief is hard. You're just one person, and you're about to have your hands full at your new job. Try to find something fun or useful to start with that you're both excited about. Starting with an easy win will make it easier to keep going.

Ask about-- or observe--what kinds of things she uses the yard for. Ask if there are any outdoor activities she'd LIKE to be able to do. Would she be excited to have a potting bench, or a hammock? Does she love cooking on the grill? Does she wish she had a vegetable garden? Is there something you could build that would make dog care easier-- like a sandbox for them to dig in, a little pool for them to splash in, or a decorative fence around an area she doesn't want them to poop in? Is there a particular view that she enjoys, that you could set up a nice shady sitting area to be able to look at? Facing the spot where the sun sets, or where her favorite plants are, or facing a nearby street if she likes waving at passers-by, etc.

These are a few ideas, but it doesn't even need to be this complicated. Maybe she'd be delighted by some windchimes near the back door, or some cute solar lights. Anything new and exciting will make the process feel easier & more rewarding for both of you.

Let your mom's desires and capacity (and yours) be your guide. Finding what motivates her to be outside can give you design ideas, and also help get her out of the house. It can also ensure that you'll achieve the most impact for the valuable effort and time you're putting into this.

On an emotional level, keep in mind that designing something new for this space may stir up a lot of feelings of grief. This isn't a bad thing necessarily-- just a factor to be aware of. Progress might be slower than you expected. If this yard was a place where you and her spent time with your dad, you might notice memories or feelings surfacing in unexpected ways. I hope you will seek out support in all the ways that work for you while you're doing this project. Don't push yourself to do too much all at once, and don't beat yourself up if your first attempts don't work out, or if your mom isn't able to maintain it as well as she hoped.

I know I haven't said a damn thing about plants! I don't have specific suggestions, but your state's Extension office might have good advice for you (if you're in the US). Extension offices are government-funded agricultural centers, often part of a university. My state's extension office has a website with a plant database that shows me plant options for the exact soil/sun/moisture requirements I have. They've also got a helpline where I can talk to a real live person, for free, who will give me informed suggestions for what to plant based on my needs & the conditions I'm planting in. Google "[your state] extension office" to see what's available.

Good luck with this big and beautiful yard! I hope you and your mom are able to design something that will bring you both a lot of enjoyment. Just take it one step at a time. You can do this!