A B737 Captain reported during taxiing they had to stop abruptly to avoid another taxiing aircraft resulting in a Flight Attendant injury.

Narrative

Our ATC instructions from Ground Control were to follow an RJ from our left to Runway XXR. We saw the RJ and began to follow it. As we were approaching the intersecting taxiway to make our turn; Ground Control advised that there was a second RJ that he wanted us to follow. As we were about to enter the intersecting taxiway; we were required to stop abruptly. After passing behind the RJ we continued out to the runway without incident. We had advised the Flight Attendants to remain seated after departure for turbulence in the area. As we were passing 18000 ft. the First Officer called to allow the Flight Attendants to start their service. At this point we were informed that a FA had hurt her wrist and ankle. We inquired if she wanted us to consult medical to get her medical attention. She decline and said she was able to perform her duties. We continued on to ZZZ1 without further incident. She was then scheduled to return to ZZZ. On the ground I assumed that everyone was seated as it had been several minutes since pushing back. I also assumed that if anything was amiss that the Flight Attendants would have called to notify us.