I would just write to her asking her to reply in writing to confirm that she will agree to divorce on the grounds of two years separation with consent ... and saying that you will get on with the necessary paperwork once you have received her confirmation.
Ive looked at them all they all relate to law in the US which is very different to England and Wales, the dead give away is "state" the post is a year old, using a US legal link will just confuse wiki members.
I know it's an old post but to answer the original question in England & Wales under the solicitor's Family Law Protocol it is considered good practise to notify the respondent of the intention to commence divorce proceedings.
It may avoid unnecessary disputes (which can be costly in terms of both money and time) if the respondent has sight of the reasons given for the marriage breaking down before receiving the petition. When there is objection to the reasons they can be negotiated into something less controversial. Also agreement about costs of the divorce can sought so there are no nasty surprises to inflame the situation later.
A Separation Agreement is something different and documents the financial arrangements spouses may wish to make when separating.