E5 form - and his new partner

If I am petitioning her as co-respondent does she have to declare her assets on the E5 form - currently she says she wont.

It is my understanding that no, she is not obliged to declare her assets on form E. In fact she does not complete a Form E at all, only your husband.

You have no claim on her assets.

The only time they come into play are:

1) For example if her assets include a house and he lives in it. Then his outgoings are reduced. So this should filter through on the Form E when he fills out his outgoings. They should be less than for someone who lives alone and pays all their own mortgage/bills.

2) If you have good reason to suspect that there are assets in her name which actually belong to him or originated from his/your marital assets. In which case you ask him for disclosure about his full list of assets - perhaps explicitly questioning whether he has other properties etc. (this questioning can be done in the form of a questionnaire sent following your receipt of his Form E).