Contemporary writers have been enthusiastic in their descriptions of Isabella; but time has sanctioned their eulogies. She was of the middle size, and well formed; with a fair complexion, auburn hair, and clear blue eyes. There was a mingled gravity and sweetness in her countenance, and a singular modesty in her mien, gracing, as it did, great firmness of purpose and earnestness of spirit. Though strongly attached to her husband, and studious of his fame, yet she always maintained her distinct rights as an allied prince. She exceeded him in beauty, personal dignity, acuteness of genius, and grandeur of soul. Combining the active, the resolute qualities of man, with the softer charities of woman, she mingled in the warlike councils of her husband, and, being inspired with a truer idea of glory, infused a more lofty and generous temper into his subtle and calculating policy.

摘自《美国语文》中学课文 第5课 Ferdinand And Isabella 费迪南德与伊莎贝拉    作者：Washington Irving

背景知识：FERDINAND AND ISABELLA were the King and Queen of Spain who supplied Columbus with ships and men to prosecute his voyage of discovery.

请教老师，There was a mingled gravity and sweetness in her countenance, and a singular modesty in her mien, gracing, as it did, great firmness of purpose and earnestness of spirit.

 此句中：

1. gracing 是状语还是定语？修饰什么？

2. as it did 是什么意思？it指代什么？

3. great firmness of purpose and earnestness of spirit 在句子中作什么成分？

4. “ great firmness of purpose and earnestness of spirit ” (目标坚定和感情诚挚)， 为什么不是 purpose of great firmness and spirit of earnestness ?  of 短语做定语应该放在被修饰的名词后面啊？这里顺序为何恰好是颠倒的？   感谢老师。