Posted: Wed Mar 24, 2021 7:34pm
If she gained Residency last July, she is tax-resident in Spain wef 1/1/21.
She will need to submit her modelo 720 in Feb 22.
She will submit her income tax return (for Jan-Dec 21) in June 22.
She will pay her income tax (for Jan-Dec 21) in 2 chunks ... June and September 22.
In October 22 she can request release from the UK tax system. This may take 6 months to achieve.
Note ... she will continue paying PAYE in the UK until she is released from the UK system. She will pay tax in Spain AND in the UK for a period of time (2 years and counting in my case). There is a cash-flow pinch point to be managed,.
In general, more income tax is paid in Spain than in the UK. Allowances are lower and rates are higher.