CGT on real property- non resident

[SDLT23]

My sister and I are joint tenants of a UK house. It is currently (and will continue to be) occupied by our mother.

I do not live there (so will be liable to CGT on my share of the proceeds if and when sold).

It was until very recently my sister's only/main residence - but she has just moved abroad permanently.

Will she have to pay UK CGT on her share of the proceeds (if and when sold)? Any recommended steps to mitigate any such CGT liability?

[maths]

The UK now levies UK CGT on UK residential property disposed of by non-UK residents.

Hence your sister will in principle be liable to UK CGT on a disposal.The liability in principle is based on market value on sale less market value as at 5 April 2015 (at 18% and/or 28%).
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However, as she has lived in the property she will be eligible for some private residence relief and an annual exempt amount of £11,100.