Dog Too Scared to Pee Outside

My family recently adopted a new dog on Sunday. She's really sweet and great, but she keeps holding in her pee all day. We take her out on more than eight walks a day, but she still won't pee outside. While I was at work yesterday, my mom walked her 2 hours over 5 miles, and she still didn't pee. She poops outside, but doesn't pee.

What usually happens is that she holds in her pee for the entire day. After the walk, she runs off to my parents' bedroom and pees on the bed or the floor while freezing up. Since my parents' bedroom was closed this morning, she ran off to pee in the basement.

Here are the reasons we think why she might be scared: -- Anxious /scared: She's always very tense on the walks and looking back at you for reassurance.

-- Thinks she's being returned: On the walk away from the house, she seems unsure and guarded, but when we're walking back home, she is practically running and smiling.

-- Finds the house safe: She only has ever peed INSIDE the house, so we think she might see it as some safe space.

-- Uncomfortable with our old dog's smell: Before her, we had two dogs. One passed away in August at the age of 18 and the other passed away more recently at almost 14 years old. Our new dog seems oddly attached to my mom's room, which is where our old dogs used to hang out most. We're wondering if she's trying to replace their smell or feels guarded by it.

-- Doesn't like being outside: She's a very curious dog and loves running around in the woods, but she hates cars and has growled at a few other people and dogs.

We've tried bringing treats on walks, having her sit down/lie down in the grass, buying a clicker, keeping her close on the walk at all times, saying "potty" a bunch, giving her a bath to see if getting rid of the shelter/pee smell would help (this was kind of just hoping anything would work), taking her out almost every hour of the day, and my mom recently bought astro turf to see if we could get her to pee on the porch because it's "home" and then slowly move the turf outside.

I'm scared she's going to get a UTI or bladder issue from holding in her pee all the time. Any help is appreciated! <3