Well, not being there to observe the bird it's always hard to say what the problem is but, going by what I know, I would say it's hungry. For one thing, the soft food you are offering is not good for a baby bird and you should never replace the formula with just pureed veggies/fruits. I have no idea why the breeder would say such a thing unless it's somebody who doesn't know enough because you never feed a baby bird a food without protein and carbs in it - it's like giving a 6 month old baby half the daily bottles with just juice in them - that baby is not going to gain weight. Have you been weighing the baby daily and keeping track of its weight? Because, if you haven't, you need to start doing it to make sure it's not losing weight. It needs two or three good feedings of formula (and make sure it's not liquidy, too - it needs to be creamy) and, what you should do is replace some of the water in the formula with pureed fruits. Don't misunderstand me, these birds are mainly fruit eaters in the wild and do need a lot of produce BUT they also need protein and carbs, especially the babies. So, yes, you do need to offer foods that have veggies and/or fruits but it also needs to have grains. Try gloop, Irish oatmeal, whole grain cous cous, whole grain pastina, polenta - stuff like that. Cook it and mix it with things like mashed sweet potatoes, bananas, grated apples, etc. You can use baby jars but do not use the ones that have cereal in them (birds should never consume any cereal that has been prepared for human consumption because they all have too much iron added to them) or the ones with spinach (again, too much iron). Give it two good handfeedings (dawn and dusk) and offer two kinds of soft food served warm and fresh twice a day. Also, put some millet in her cage, too - it's a nice, soft, small seed that they like a lot and it has carbs and low protein - perfect for a baby. As to feeding her Zupreem pellets... well, for one thing I do hope they are not the colored ones which are, without exception, the worst food you can give a parrot (lots and lots of bad things in them). I do not recommend anybody feeds pellets to any bird except maybe chickens but, if you have your heart set on pellets, at least get Tops and wet them before you serve them (pellets are a max of 10% moisture while parrots natural diets are 85 - 95% moisture).
It is very unfortunate that you clipped such a young bird...but, if she can still fly, it should be OK because when they are clipped before they learn, they never develop all the necessary neural paths in her brain and will never fly well. One of my GCCs was clipped as a baby and kept clipped until she came to me at 18 months of age and even though she can fly after a fashion, she only does it when she has no other choice and very badly at that. As to how to keep a bird from flying off the door... well, I have buffer zones: porch for the front door and mud room for the back - but I don't have children going in and out, either and I am a maniac when it comes to opening the doors when they are out flying (it's pretty much forbidden in my house). If you do not have buffer zones, I suggest you keep her in a room that has no 'outside' door in it so, if she does fly through the door, she will end up just in another room. I also suggest you get those magnet screens for the doors that close by themselves once the person went through and a sign on the door to the room where she is kept saying something like :BIRD IS OUT - DO NOT OPEN DOOR!
Also, please, NEVER cover a bird's cage during the day - NEVER NEVER NEVER. I know that this is something that people used to do but we have learned a lot since those times and we now know it's bad for them. Let me explain. Birds are all photoperiodic (research avian photoperiodism, avian endocrine system and avian reproductive system) and depend on the quality and amount of daylight hours to set their internal clock that governs their endocrine system (the light of dawn turns on the 'stop watch', the light of dusk turns it off). When you cover a cage during the day, you are interrupting the 'workings of the clock' and messing things up. Birds know when to eat (dawn and dusk), when to rest (noon), when to breed, when to molt, when to migrate, etc based on the light they receive during the day (research circadian and circannual cycles) so in order to keep them healthy and happy (lack of light depresses them) they need to be kept at a strict solar schedule with full exposure (two hours) of dawn and dusk (without any artificial lights on before the sunshine is streaming into the room or after the sun is halfway down to the horizon in the afternoon). So, when you cover the cage in the middle of the day, you are messing up the circadian cycle and confusing its body.
Also, please do not try to potty train it. It's extremely harmful to birds which have a super fast metabolism and need to poop every few minutes (little birds do it every 20 minutes during the am). Birds pee and poop in one single deposition and when you train them to 'hold' it, you are creating a situation that nature never considered and there are a lot of birds that end up with cloacal prolapse because of it. Parrots are not dogs and should never be housebroken but even if they were like dogs, even adult little dogs cannot hold it for more than a few hours at a time (and that's why toy breeds are usually trained to go on a wee wee pad). Birds do poop all over the place but this is part of living with a parrot. I have plastic covers on all my tables and old quilts and bedspreads covering my sofas and chairs which get changed and laundered every couple of days and I just scrape the poop off the floor, moldings, etc, mist with a spray bottle, wait a few minutes and then mop or wipe. It's a bit more work but this way, my furniture is 'saved', my house is clean and my birds are healthy.
Living with a bird means making A LOT of changes to our 'normal' lifestyles... people see them small and think that because they 'live' in a cage they are low maintenance but, in reality, they are super high maintenance and, in all honesty, I find it's less work to have 20 dogs or 40 cats than two parrots

For one thing, with dogs and cats only I would be able to go on vacations, receive people in the winter evenings and go visit relatives that live far away often - all things I cannot do because of the parrots...