I don't know if she doesn't run off with your materia then. By the way the MP Absorb Materia is in the Item-shop and the HP Absorb-Materia is in the cathouse. You cannot get the HP Absorb-Materia untill you finished the sidequest. But you have to be on the sidequest then, if I am correct. But there are more materia's then only those two. In the cavern on the mountain you can get Steal As Well-Materia (If you got the Levithian Scales in the Underwater Reactor at Junon. And didn't forget them, like me X-x). And if you do the sidequest in the Pagode (after you did the complete Yuffie-sidequest) then you will get the summon-materia from Levitihian.

If you are on disc 3 some scenes during the sidequest can be confusing, but don't forget it was actually ment to begin right after you stole the Tiny Bronco.