Complex sentence: Catherine played little part in the politics of Tyrol; moreover, a former lover of Sigismund intrigued against the young bride and falsely claimed in 1487 that Catherine was trying to poison her husband.
Split into simpler sentences: Catherine played little part in the politics of Tyrol. A former lover Sigismund who was against the young bride falsely claimed in 1487 that Catherine was trying to poison her husband.