Is this a flexible working request?

A member of the admin team is contracted for 15 hours per week working these across 2 days, which is what the post was advertised as and what the service requires. 

The employee has been working at home through lockdown, but June onwards we will be bringing staff back for a % of their contractual working hours to be worked from site base. They have requested that on the 1 day a week they are on site, they leave base at 2pm to pick up children from school at 3.15pm and then log back on and finish working from home. The employee states that they cannot afford to pay for the children to attend the afterschool club. Technically this would mean approx. 90 minutes out of the working day, but with the time not being made up due to childcare commitments. The supervisor has raised that this means they will not be available to take telephone calls (we are a very busy service and this person is first point of contact) and would also be unable to provide admin support to team members if it was requested and it would fall to themselves or another team member to cover. In addition, the supervisor has also raised that the employee will not do certain tasks at home because of confidence etc. 

Due to the nature of the service, it would be difficult to alter the working pattern of this staff member, but I was just wondering what processes would be best to follow under these circumstances, particularly around the childcare issue?