You haven't told us anything about either case, so there is no way we can tell you whether or how they might interfere with each other.

Courts do indeed have the authority to consolidate closely-related cases, assuming that the same court has jurisdiction over, and is the appropriate venue for, both. Ordinarily this will only happen if one of the parties asks for it and persuades the court hearing her case that it should be combined with the other. Parties who don't want the cases consolidated can oppose the motion.

I believe courts have the authority to order cases consolidated even if nobody asks them to. Offhand, though, I am not sure.

If the case against the person omitted from the complaint arise from the same facts and circumstances as the first, the omitted person should be added to the original suit. All attorneys name what are known as "DOE" defendants so that if a new party is discovered that party can be added without bringing a separate action and without worrying about the statute of limitation. If your attorney did not add the omitted person she probably had a good reason (perhaps she does not feel a case exists against this person) so you should ask her why the person was omitted. If you bring another lawsuit against this other person, the court has the authority to consilidate both actions on its own motion, or on the motion of any party to the lawsuit; hence, a new lawsuit will likely be consolidated.

Speak with your attorney first, as she will be upset if you go behind her back.