Wife left me after few months of marriage. How to divorce her?

You cannot file divorce before June 2015 because as per  Section 14 of the Hindu Marriage Act, 1955 provides: - No petition for divorce to be presented within one year of marriage. -

(1) notwithstanding anything contained in this Act, it shall not be competent for any Court to entertain any petition for dissolution of marriage by a decree of divorce, unless at the date of the presentation of the petition one year has elapsed since the date of the marriage: 

Thereafter you have to options to file divorce, first option is to file a  Mutual Consent under Section 13 B of Hindu Marriage Act. This process can only happen when both the parties amicable decide to file divorce on their mutual terms. This process is faster and less time consuming

Incase she does not agree, then you can file divorce under Section 13(1) on the ground on cruelty. However incase of contested divorce she can file application under Section 125 CRPC thereby seeking maintenance for herself and for step daughter.

Also if your property is self acquired then as per the judgement of Supreme Court she can claim right to residence in the said property.