Invitation letter for S1 visa

invitation letter from yourself is enough, but make sure it should include following details:
a) Information on the applicant (full name, gender, date of birth, etc.)

b) Information on the visit (purpose of visit, arrival and departure dates, place of intended residence, relations between the applicant and the inviting individual, financial source for expenditures, etc.)

c) Information on the inviting individual (name, contact telephone number, address, signature, etc.)

BTW, you need to send her a opy of your passport and residence permit.