I'm leaving for a student exchange to France for three months. My sister will be coming along with me for a week. So I have added her name under the list of Airbnb guest members for her accommodation proof. She comes for 7 days only, but the Airbnb booking is for 90 days. Should that be an issue for her visa? She has applied for a tourist visa. She will also tour around with me for the initial days.
As long as you are truthful and bring all the evidence you need, you should not have a problem with this situation. You sister is staying for 7 days so she will have a booked return flight ticket to prove this. If your sister can also demonstrate strong ties to her home country, then this will help convincing the immigration officer reviewing her application that she has genuine intentions of returning to her home country at the end of her stay. These include, and are not limited to:
- A permanent job
- A house in which one lives / pays mortgage
- Family obligations - children, family members to look after
Strong ties can typically be demonstrated by the provenance of the funds used as evidence to support one's stay in the country: if there is a regular income of funds from a reputable source then it is likely that the applicant is employed/has stable revenue, both of which indicate a stable lifestyle at home.
In short, do not overthink this. All you have to do is present a strong case supported by truthful evidence.