All Pelosi wants is to get rid of Trump and keep the speakership. To ascribe any principles to her actions would be giving her far too much credit.
She wants to take out Pence too and become POTUS.
She just wants to keep her speakership. She is trying to score points with her leftwing base by fighting Trump on every issue.
Her problem is that Trump is framing these fights and she is falling into traps. She was going against public opinion on impeachment and now is going against it again on war with Syria. The democrats are screwed.