There's no USPSA division in which the 9mm Hi Power can be competitive. Also, the ergonomics aren't actually that great. While the trigger is single action, it has massive over travel and a long indistinct reset.
As you say, the trigger just isn't very good. I've tried a Hi Power and wanted to like it, given my reverence for St. John Moses, but I just couldn't.
For starting out in USPSA and IDPA, pick whichever you like better between the Glock 17 or 34, on M&P 9 full size or pro. I've heard good things too about the new 5.25 competition XD, but haven't seen one yet.
Another alternative is to just start out with the M&P compact. By the time the OP feels it is holding her back, she may have a better handle on what she wants.