Painting - lines noticeable after paint has dried

I just painted a second coat on my daughter's walls and the line where the roller meets the "cutting in" is completely noticeable. It was not obvious with the first coat but now that the second coat is on and dry, you can completely notice where the roller ends and the brush begins. Is there anything one can do to blend it better? Can I take a brush with a light coat of paint on it and try to "feather" between the two without painting an entire 3rd coat or do I need to do the entire process over? It I do have to do another full coat, any recommendations on how to blend the two better?

it is usually best to use a small ,or large if you can handle it, roller and go side ways at the top. This will do 2 things. It will give the roller texture to that area that was previously brushed and it will get rid of the build up that you have. If it was me I would probably wait till it cured enough to sand[ maybe 2 weeks +] and sand it and try to just touch up the top. I am sure you could try some goof off or something to disolve it but since I have never done it I can't say. I don't think adding another coat will make it disappear. I would wait and sand it.

What you are seeing is called 'hat banding'. Yeah, like joneq said, we do what is called a 'french cut'. After brushing out the edges of the room, we use a 2' step ladder as we roll it, and climb up and roll sideways as close to the ceiling as possible. Actually, we do this for all edges.

If you are using a strong color or a glossy paint, it might be from losing the edge. I cut the cielings on one wall then roll the wall like PWG described. Then go to the next wall.