Permanent transfer from Manchester to Chicago at the employee's request: what is reasonable?

A senior data scientist has asked to move permanently to our Chicago office because her partner has taken a job there. She is highly rated and we would rather keep her. We are an insurance group of about 8,000, and our only international policy is the full assignment one, which is clearly not right for a one-way move she has asked for.

My draft is: US local salary and benefits from day one, visa and immigration costs, flights, 30 days of temporary housing, a shipment allowance of GBP 6,000 and tax advice for the year of the move. No housing support, no home leave.

Is that mean, generous or about right for an employee-initiated transfer?