watch it again its explained quite well why she can do it good episode
look at the power the daleks had at their disposal now imagine it in the hands of a timelord
i dont see the problem i mean davros even says a time lord without a weapon is still a dangerous thing hence the force field cell hes put into look at the power the daleks had at their disposal now imagine it in the hands of a timelord not as far fetched now is it as far as the daleks know the doctor is the last time lord and davros had assumed hed killed donna
have to remember the time lords were the equal of the daleks if not better not killing a companion was a bit of a cop out but we did lose 2 companions we lost rose we probably wont hear from her again and donna is gone for good