You certainly cannot house a Bearded Dragon (DESERT REPTILE) with an Iguana (TROPICAL REPTILE) for 1,000 different reason, the biggest being they iguana would literally eat the Bearded Dragon, but I'm trying to show you the basic idea that doesn't work here with this example, lol. Desert Reptile with a Tropical Reptile. Two totally different environments, temps, etc. No.
Please don't house ANY OTHER SPECIES OF ANYTHING WITH YOUR BEARDIE!!! If you were even considering putting an Iguana in with your Bearded Dragon, then I'm sorry but it's obvious you don't have much knowledge of lizards to begin with, and I'm saying this not to be mean, but to point out why this is a really bad idea.
The number one reason to leave your Beardie alone in her Viv by herself is because that's what she wants, that's how they live naturally, they are solitary animals, and as already mentioned other than putting a female with a female it doesn't work, and certainly not with any other species of reptile.
You need to realize that in most cases, if you put another species of lizard in with your bearded dragon, you bearded dragon is going to be the submissive lizard that is killed/eaten...so fair warning.
And by the way, iguanas grow up to 10 feet long and require an entire room to live in, with totally different lighting/temps/diet and everything else than a dragon. Just as any type of monitor or Tegu is going to as well. So for the sake of your dragon please, just leave her be by herself.