Cloth nappies gone bad?

Are you leaving them on longer than normal?

a nappy will normally leak because the fit isn't right and there are gaps or they are being left on too long or your child is weeing more (which is normal as they grow).

When you take the nappy off, is the whole nappy/insert wet/soaking or is only just some of it wet?

How is the leg elastic holding up? I had this problem when the leg elastic started to go in some of my nappies. Also again recently because there is a build up of cream on the liners so the pee is running off instead of through. That will be fixed by replacing the liners though.

what about a strip wash?? using nappy cream and laundry detergents can build up and reduce the absorbancy, stripping them will restore their absorbancy

I had some creams in my babys cloth nappies when i had been forgetting to use a liner to protect them and so i put them in a hot wash to get rid of it but they still didnt absorb as well so i soaked them for 24 hours in cold water and they went back to normal. I use BabyFirst brand. But it sounds like she may be holding it for all at one as stated above or may be wiggling in a way that they slide around on her? Try adding a certain amount of water onto them to see if its really her having a big pee or not absorbing much i did that when i realised it was the cream building up.