The DS-160 is an online form. Either one of you can fill it out. Id suggest working on it together and gathering all your documents first because it's not the easiest form to get done. I know because Ive already submitted my fiance's DS-160 along with her son's. The embassy will want a form DS-160 completed online for EACH applicant, including all children that will also be receiving a visa. If your fiancée will be bringing 4 children, then you will need to complete and submit a DS-160 for all 4 children, plus your fiancée. The DS-160 will require the ALIEN to upload a 2x2 passport size photo of the ALIEN with a white background. You must upload a picture or it will not allow you to submit. When you have completed the form and uploaded the picture you will click the SUBMIT BUTTON. Once you submit it, it will be sent directly to the US State Department and it will instantly provide you with a confirmation page. You MUST print the confirmation page (or choose the email option to print later) and take it to your embassy interview. They do not want you to bring the entire form, they only want you to bring the confirmation page. Special Note: If you spend too long on any page the system will think you are no longer there and it will time out and you will lose everything on that page and have to start over, so try to move quickly through it.
DS-160 online form https://ceac.state.gov/GenNIV/Default.aspx
Instructions https://ceac.state.gov/GenNIV/Common/Instructions.aspx
FAQ's https://travel.state.gov/content/travel/en/us-visas/visa-information-resources/forms/ds-160-online-nonimmigrant-visa-application/ds-160-faqs.html
Digital image requirements https://travel.state.gov/content/travel/en/us-visas/visa-information-resources/photos/digital-image-requirements.html