Well a couple of possibilities;
1) A stray shot from Kallus sets off the bomb and Tua simply accompanies the Rebels although I can't see Kallus not continuing in pursuit since the whole point of the charade was to blacken the rebels name.
2) She survived the blast and was left for dead by the rebels but I can't see the Empire saving her since her being killed was the means by which they would ruin the reputation of the rebels,
3) She survived and is thought dead by both becoming an underworld figure seeking vengeance against both using the information she knows with dreadful effect!
4) It wasn't her but a double, the whole calling in the rebels was to set them up and stage the bombing herself so whilst they saw her enter the shuttle she jumped beneath and escaped through the other side of the hangar whilst Kallus thinking it was part of Vader's plan took advantage with neither paying attention to what was actually going on.
Vader of course assumed either Tarkin or Kallus was responsible and none of them bothered to double check if that was the case...
Well that one could actually work as long as Tua left the planet and had plastic surgery and a complete change in habits to avoid being noticed...
This would actually be a nice call back in a Rebels episode if they discover it was all a set up by Tua to escape the Empire's clutches!
