The events are (presumably) independent: $$\mathrm{Pr}[\text{someone else having a bomb}]=\mathrm{Pr}[\text{someone else having a bomb}|\text{old woman has a bomb}].$$
The fact that the old woman has a bomb makes no difference to the probability of someone else having a bomb (unless, say, she happens to be with a terrorist organisation and tends to fly with other terrorists).