Well, you answered my shit so I may as well contribute what I know. Never dated anyone immobile but I have dated someone who was pretty much housebound, took maybe less than 250 steps a day & was planted on her couch for most of it. I love USSBBWs and I will always be a connoisseur of those ladies, but I'm with someone who can shop at Old Navy these days and can honestly say I'm fine with leaving it as a fetish online.
She's going to be bored. A lot. You will be responsible for providing a lot of her entertainment, whether that's curiosities, games, or forms of media to enjoy. Expect a lot of movies & TV with her - it's not like she's going anywhere.
Assuming you two have met and this is a physical relationship, this is going to be one-sided as you will be more of a caretaker than an equal partner. It's not a drag on her, it's just reality - she can't cook for you, help with small tasks, hell she is going to depend on you to help her with pretty much everything. Not all at once and certainly not at first - you're not going to wipe her ass. But eventually you'll start helping to dress her if you haven't already. Next you may need to help her dress a wound or apply balm. Long term, it'll be ass wiping. You'll need to mentally prepare yourself to be a bit of a CNA.
She's going to get depressed. You've probably already been exposed to this already, it comes hand in hand with the boredom. She's going to be 32 and she hasn't left her bed in years, she almost died, and she's over 500lbs. Honestly that's a damn low spot for anyone in her position. You can be as supportive as you want, it's still going to happen and she may latch to you for emotional support. How you decide to handle that is your business, I would just be prepared to put on a therapist hat.
It's going to be different than any relationship you've had in the past because she's not independent, not one bit. I'm happy you two are in love, I'm not trying to rain on your parade here. Hope you like Instagram reels and TikTok, because that's going to be her love language since going on walks or out to dinner or even sitting on the porch smoking a J is out of the question.