The ahsan talaq involves a single revocable pronouncement of divorce and sexual abstinence during the waiting period. The hasan divorce involves three pronouncements made during the wife's state of ritual purity with menstrual periods intervening between them, and no intercourse having taken place during that time.
The iddah of a woman divorced by her husband is three monthly periods,unless she is pregnant in which case the ‘iddah lasts until she gives birth, or unless the marriage was not consummated in which case there is no `iddah, or unless she does not menstruate, in which case "the scholars say that she should observe an ‘iddah of a full year, nine months for pregnancy and three months for ‘iddah.
The initial declaration of talaq is a revocable repudiation (ṭalāq rajʿah) which does not terminate the marriage. The husband can revoke the repudiation at any time during the waiting period (‘iddah) which lasts three full menstrual cycles. The waiting period is intended to give the couple an opportunity for reconciliation, and also a means to ensure that the wife is not pregnant. Resumption of sexual relations automatically retracts the repudiation. The wife retains all her rights during the waiting period. The divorce becomes final when the waiting period expires. This is called a "minor" divorce (al-baynuna al-sughra) and the couple can remarry. If the husband repudiates his wife for the third time, it triggers a "major" divorce (al-baynuna al-kubra), after which the couple cannot remarry without an intervening consummated marriage to another man. This is known as tahlil or nikah halala. Making the third pronouncement irrevocable prevents the husband from using repeated declarations and revocations of divorce as a means of pressuring his wife into making financial concessions in order to "purchase her freedom". It also acts as a deterrent to rash repudiations.
Therefore you can send your decision of talaq in writing to her with one or two witnesses by registered post and can follow the above procedures for making it final by which your marriage will get dissolved automatically after the completion of the iddah period.