When it shows signs of over watering, they only need about an inch a week after being established. When they are new or transplanted water daily for a week, than give it an inch of water a week. If it rains an inch, you’re done for week unless it’s stupid dry and starts showing signs of needing water (obviously).

Every day is probably too much, unless you’re in a dry area and they’re very well drained. I’d describe watering as saturating, not flooding, and let it dry to the roots, not just the surface, before watering again. Dry, but not completely moistureless bone dry

Also, on hot sunny days, water in the evening or early morning, else you’ll just lose a lot of water to sun evaporation.

You could always get a moisture probe. I’ve found it extremely useful

I doubt it’s over watering, due to the fact the others look healthy enough. Dig up the root ball of that one, look for pests in there would be my first step to diagnosing.