Can I just ask why you are trying to drop the NF? Does DD not seem hungry? It is still very normal for a 4 mo to still need a NF, especially of you are still trying to transition to a 4hr EASY. If DD can't manage to go longer than 3.5 hrs in the day then it is expecting quite a lot for her to go all night without a feed yk?
Have you seen the link that I posted about just adding 5mins on everyday? This might help your DD. Also it is quite common for LOs to transition from 3 to 3.5 hr easy and then after a while of 3.5 hr move to 4hr. So it is great that you have got to 3.5 hr, maybe your DD needs to stick at that for a while. Have you pushed her A times a little too? How has that effected the NW?