Re: First signs of irritation, help!!
Does the redness stick around or go away? Does she let you know that it's painful?
I'd use lanolin over coconut oil for night, because the lanolin is closer to skin's natural oils, and it helps break down urine into water.
If you can try that diaper combo during the day, and see if they smell strongly right when she pees on them ... then it suggests you have some buildup issues. There are an overwhelming number of possible solutions for that, but boiling the inserts is a good start. After years of trying other stuff, I only ever use cotton flats at night, with a very thin hemp doubler, because they're so easy to get clean. The hemp doubler gets rinsed first thing in the morning.
If the diaper makes your eyes burn when you take it off, you're getting some ammonia. This can be from buildup, but it's also just what happens to urine over time, especially without air and with warmth. The night diaper with a PUL cover is the perfect storm for accelerating ammonia.
If you think that's the problem, you can try a fleece or wool cover.
It definitely sounds like you need more absorbency.