It's her family details. They don't ask for the sponsor's family details anywhere on the online form or VAF4a Appendix 2.
Looking at the paper version of the online form, it asks for:
- Applicant's personal details
- Applicant's passport details
- Applicant's contact details
- Applicant's family information
- Applicant's travel/criminal history
- Applicant's UK sponsor details
- English Language requirement
And then the VAF4a Appendix 2 form asks for:
- Relationship to the UK sponsor
- Future accommodation in the UK
- How the UK sponsor meets the financial requirement