What should I do about my sick cat?

Hi everyone. My cat is very sick and close to dying and I need advice. I don’t want her to suffer, but I love her and obviously don’t want to have to do that and Id feel so horrible for not just letting her live out the rest of her life in her home where she’s comfortable. We’ve had her since November of 2020 and she’s now two and four months. She was very skinny when we first got her and she began to put on a little weight after a while, but then she got a bacterial infection and we were able to treat it, but she was still pretty small. I have a feeling she was abused at her last home because she’s always been shy and hiding in the bathroom at our last home all of the time and now at this home she’s always in our bedroom. She’s comfortable around me and will be out, but if anyone else even walks by she runs under the bed. Well over the past maybe 4–5 months she’s been losing more weight and the last vet visit she was 3.9 lbs. When I noticed she was losing weight, I took the advice from those around me and started giving her only wet kitten food with a little hard food because I didn’t want her teeth to rot. She just continued to lose weight and we found out that she’s severely anemic and she has a parasite in her blood that causes her body to attack her blood. Due to the toxins in her body, she’s going blind and it’s getting worse day by day. Her pupils are fully dilated, even when you shine a bright light directly into her eyes. It began with her pupils being different sizes and having little reaction to light, but they still had some. Now that’s just totally gone and she’s walking straight off the bed, walking into furniture and tripping over everything and she’s very wobbly. I just sit with her and keep her steady and give her some company and tlc. She had developed a respiratory infection and our vet put her on an antibiotic and steroid so to help with the respiratory infection and the parasite in her blood. Since we began giving her the medicine, she’s been out a lot more, been more receiving to love from both my boyfriend and I, and she’s even wandering out into the living room. When she’s startled now, she just freezes and looks very tense. The past two days she seems very hungry for food and will scarf about half of what she’s given and then stop eating and she won’t drink water (at least not that I’ve seen). I’ve tried putting it in a syringe so that I know she’s getting water, but she already hates having to do that with the antibiotic and steroid and when I give those to her, she starts wheezing more like it went down wrong or it’s just really thick or something. We’ve taken her to the vet many times to get antibiotics for bacterial infections and she’s up to date on her vaccinations. I’m just very sad that it’s happening like this and the vet said that it’s always a possibility (which is why we took the meds) that she can get better and just live out the rest of her life blind just fine, but that she’ll more likely than not get much better and that we’ll have to choose euthanasia. I’d just really hate to do that to her in a noisy office somewhere she’s totally unfamiliar with, especially since she can’t see anymore. I’d like to let her live her life to the end in her home surrounded by familiarity and comfort and love, but I don’t want her to have to suffer like that, but I also don’t want to feel like I’m playing god and mess with nature like that. I just don’t know what to do, so any advice would be greatly appreciated, whether I should go in office and go through with euthanasia or let her stay home.