Stacking save penalties is a well-known way to break 4e, but it's not strong enough to make a solo, invincible character. There are a bunch of things about the described character that are either illegal or don't work as intended. Some of these have been covered in other comments, but here's the list of everything I can see:
1. This isn't explicitly stated, but the plan against regular enemies is to run in, apply Fire Shroud damage to one guy, run away and hide for 5 minutes, then come back when he's dead and do the same thing to the next guy, right? (If not, all those save penalties won't apply as stated.) The big problem with this, of course, is that the enemies can go find reinforcements, continue killing innocent villagers, run away and hide with all their loot, etc. in the meantime. Or prepare to slam the door behind her when she comes in next time, so she can't run or teleport away.
But even purely mechanically, this won't work. Say you have a standard encounter of 5 creatures. The munchkin wizard sets one on fire and runs away. The other 4 can then use Heal checks to each give a +2 bonus to the burning guy's next saving throw, and it can (perhaps after a few tries) save with a +8 bonus and survive.
2. If Orb of Imposition is used with sleep, it can apply a save penalty to either the slowed condition or the unconscious condition but not both. If she uses the save penalty to make sure the target falls asleep in the first place (by applying it to the slowed condition), then the target doesn't get the extra penalty against the unconscious condition and can wake up quickly.
3. She can only have one copy of Sleep prepared per day. As FireLance mentioned, PHB 158 states "You can't prepare the same spell twice." And when choosing powers, PHB 27 states "You can take each power only once".
4. Veteran's Armor was errata'd to remove the ability that trades an action point for a daily power. She can use Salve of Power instead (for Sleep only), but those cost a lot more.
5. The gear selection is illegal. A nightmare is not a magic item and can't be selected for the level 16 slot. It costs 25,000g, which would use up all of the gold available to a level 16 character.