Going by the description of her race, that wasnt a bad plan, her entire thing is basically being a master at instantly accessing all needed knowledge and perfectly controlling the body she inhabits, so if it wasnt for the orbs literally rejecting her, she would have absolutely already gotten away and/or caused havoc. That doesnt mean a backup plan wouldnt have been a good idea, im just saying that this was totally unforeseen as an obstacle and the plan itself had a very high chance of working. On top of that, she has a hostage to delay and weaken any potential responses as she has hijacked sydneys body and her mind is still there and thus savable.