Drywall compound doesn't stick to paint well and will bubble, so you need to CAREFULLY get rid of the paint without fuzzing or damaging the drywall, and then use normal taping techniques. I've had to do this a number of times for repairs.

I've had to fix the similar things a number of times. Here's about the easiest way to do it properly:

1. Sand the area down to get rid of any loose stuff, chips, etc. You don't have to over-do it, just get it basically smooth.

2. Wipe the wall with a damp sponge and let it dry. This gets rid of the dust so the tape in the next step will say put.

3. Cover the seam with fiberglass tape. Extend the tape a bit past the ends of the problem area.

4. Apply a coat of drywall compound with 4" to 6" taping knife. Get it on there basically smooth and don't tounch it until it's dry. If you play with it a lot, it will get nasty and fuzzy.

5. Sad it down a bit, wipe it, and apply another coat.

6. You should be good to paint it after this. If there is texture on the wall, get a can of spray texture and match it. Practice on piece of cardboard first to get the hang of it.

If things don't go right, then sand them down a bit and try again. It's doable, just be patient.

Does it move around when you push on it? Sometimes when hackers do repairs, the drywall isn't fastened properly (could also be why the two seams aren't matching). If it's not moving around, then I would just mesh tape the seam and then skim coat over the whole area...you may need to do a wide patch to disguise a hump if there is one. If it is moving around, then you should add screws to get it secure, or the real correct way would be to remove it and add some wood or cut out the drywall all the way to the studs so that the new piece can be screwed in place the right way.

I'm more concerned as to why the repair is there in the first place. Was the window leaking and replaced and/or re-flashed? If so is it fixed?

The drywall is secure. I have no idea why they pulled the original drywall out, but it was not a leak - if it were, the area right under the window would have been the worst. This is a section about 4' long from the floor up to about 3" below the window sill. I assume somebody kicked a hole in the wall there or something. It may have been cracked, or otherwise damaged, but there is no sign of any water damage. Had I needed to remove a section of drywall like that, I'd have removed the ENTIRE section all the way up to the sill - then there would have been no need to tape it, at least not along that top edge. They must have taped it along the vertical seams since all that looks normal.

However it certainly sounds like this is beyond my skill set, and certainly outside of the time frame I have to get things done around here. I don't have 3 days to spend on this - especially when its almost certain to take me much longer and/or that I will have to repeat the process trying to get it right. It'll just have to stay the way it is unless the magical wallboard fairies fix it for me one night, LOL!

I figured that would be the case. Sadly. Thanks for the help.

It won't take 3 8-hour days to do it. It will just spread out over 3 days because of drying time.

And if you want to cut down on the drying time, you can try using the powdered stuff that you mix with water and it sets in an hour.

That's a chemical reaction that makes the mud hard as opposed to having to wait for it to dry completely.

They've got 20 minute mud nowadays.

They actually have 5 minute, too. I ain't been that fast at doing anything since a teenager.

Hot mud(quick dry) needs a bit of practice. I remember the first time I tried it---was not good. I did learn a whole lot about sanding drywall mud, however. :-)

Buy or borrow a curved drywall trowel. It will reduce troweling time, sanding time and produce a smoother patch. Paper tape is often more forgiving.

I have plenty of time so I don't mind waiting a day between coats.

If a butt joint, lol at using a 4 or 6 inch knife. More like two passes with a 12 or 14 to achieve smooth unnoticeable joint (tapered vs butt joint)

You can repair this...like frosting a cake! T. Farewell gave you the basic steps.

My dad, a union plasterer/lather, taught me to use the old kind of bottle opener with the pointed v-shaped end before I put on the fiberglass mesh tape. Simply run it along the crack to gouge out a small trough then place the mesh tape over the crack. Use many THIN coats to build up a smooth surface to sand. I use a wet sand sponge. I had MANY cracks to repair...none of them have re-cracked. Thin coats and dry thoroughly between coats!