Complex sentence: She cited Republican partisanship and overlaps with the Democratic party platform as factors in making this decision and said that she had received 470 letters from constituents weighing in on the decision, with approximately three-quarters supporting the switch.
Split into simpler sentences: She cited Republican partisanship and overlaps with the Democratic party platform as factors in making this decision. Seeking feedback from her constituents, she received more than 470 letters weighing in on her decision to leave the GOP, with approximately three-quarters supporting the switch.