▲你的句子可作如下改写：

On her birthday, there was held a splendid party.

=On her birthday, a splendid party was held. 她生日那天举行了盛大的晚会。

▲你的句子属于there be句式与被动语态的“混搭”，其句意与普通的被动语态意思相同。又如：

1. There was born a child. 

= A child was born. 

有个孩子出生了。

2. There were found various relies of Franklin’s expedition.

= Various relies of Franklin’s expedition were found. 

发现了富兰克林探险的各种遗迹。

3. There are now published thousands and millions of books every year.

= Thousands and millions of books are now published every year.

现在每年出版上亿册书。

4. In recent years there has been produced more food than the country needs.

= In recent years more food than the country needs has been produced. 

最近几年生产了超过国家需要的粮食。