My Cat is Peeing on My Bed

I have two cats. Aurora is the one with the issue. She is 2, and I adopted her 6 months ago. Artemis is my other cat. She is 4 and a half-ish, and I adopted her when she was about a year old. I rescued both, so I don't have exact ages or breed info, though Aurora has a smushed face and stocky body like a Persian. They are both considered former feral cats, though both failed pretty hard at taking care of themselves on the streets.

The issue is that Aurora pees frequently on my bed. Half the time when I am sleeping in it. She has done this literally since day one. I don't think she's doing it because she has a grudge or wants to punish me, but it's a behavior that I want to end for obvious reasons.

The only place she inappropriately pees is in my bed and on two occasions my normal spot on the couch and twice on my chair. Everything she pees on is treated immediately with enzymatic cleaner from Nature's Miracle.

For background, when I adopted Aurora she had just finished weaning her 9 week old kittens, weighed only 6.3lbs, and had lived in an Arby's dumpster for nearly a year, from kittenhood to when the rescue took her in. The rescue was hesitant about letting me adopt her because they were worried that she might be skittish or aggressive, but I had experience with Artemis, who is a former feral and was very skittish for quite a long time and the fact that I lived alone so there would be less people to overwhelm her in the new environment. 

Her foster mom took her to the vet for a check up and spay the day before I took her home. I took her to the vet a week later. He found that she was running a high fever, had a sinus infection, and a vaginal infection with discharge. Her infections cleared up fully in about two weeks. I also went through the slow introduction process to introduce her and Artemis over the course of about a month. 

I had issues with her peeing on my bed, like I said, from day one, but I assumed they were just from the ridiculous amount of stress going on in her life. 

I took her to the vet after about abou a month and a half of having her to get it checked out. She did have a UTI and struvite crystals her urine. I have taken her to the vet several times to follow up and check if there are issues. She has had labs run on her urine three times. She has only had issues one time since that initial visit and that was when I switched her off of her prescription diet (to Solid Gold, so a premium brand just not prescription).

They did just raise the price of the prescription food, and I can't afford it, so I'm in the process of switching her to the Wholehearted Urinary formula from Petco. I haven't been able to get her to eat anything but kibble, though I know wet food would be better for her.

I also use bottled water that is then filtered again by the two cat drinking fountains in my apartment. She drinks lots of water over the course of a day and urinates regularly.

I have 4 litter boxes. She uses all of them in addition to her inappropriate elimination. I experimented with different litters. I found she is unwilling to use the litterbox if there are any clumps in it from urine or poo, so I use a non-clumping silica litter and check/scoop the boxes before and after work and again before bed. Her favorite is the smallest one that's in the bathroom.

Personality wise, Aurora is, as my vet put it, "flawless." She transferred her maternal energy onto me, she grooms me, cuddles me, and even puts herself between me and anything she finds scary, like noises in the hall and groceries when I bring them home. She is incredibly friendly with every human she comes across and loves to sleep on laps, play with toys, and wants to be close to people. I always make sure to give her outs, but she chooses to cuddle with complete strangers within minutes of meeting them. She greets my vet every time by jumping out of her carrier, getting on her hind legs, and bunting her face against him.

Aurora and Artemis had some minor issues when they were first being introduced. They had a hard time reading each other's body language, and Aurora kept trying to play too rough for Artemis, who was intimidated by her. But they have developed a great relationship with each other and like to hang out flopped on their sides, approximately one foot apart, to groom themselves or nap. 

I just... What am I doing wrong? What can I do to fix this issue? I'm spending a small fortune on enzymatic cleaner and just got woken up yesterday morning at 4am (again) because Aurora was peeing on my mattress about a foot away from me. At this point, I flip my mattress on it's side after I wake up and don't flip it down until I'm getting ready for bed, and I put double sided tape on the couch and chair when I'm not using them. I was locking her up in the bathroom at night, but it just made her seem stressed out during the day and wasn't solving the problem. She's healthy; I think she's at least somewhat happy; and she has all the resources I can give her.