I have no idea if Bella is suffering from this, but it sounds very much like it. I rescued her at 5 years and after a year or so, I noticed that one of her pupils was slightly larger than the other. I took her to the vet who examined her eye closely, tested it to ensure that she didn't have an ulcer or cataracts & said that obviously something was going on, but she had no idea what it was. Possibly something that was caused by an earlier trauma. As it seemed to be causing her no pain, we decided to leave alone.
Fast forward 6 years and now at 12 that pupil is permanently dilated. I think it's been so gradual that she has gradually adjusted and coped with it well. She misses the ball if we throw it past that side of her but mostly she turns her head to compensate.
She's not entirely happy at dusk, but is perfectly happy at night time. She does squint in the sun, but I think she always has. Occasionally her 'bad' eye gets a little gunky with debris, (especially if she has been snuffling around in undergrowth), which I clear by catching the edge of it with a cotton bud and then twist it away from and out of her eye (without touching her eyeball). Have not seen any sign of infection, or distress at all-touch wood.
The other eye may be heading the same way, but is some way behind I think.