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If you are a joint owner of the property then this property not being your main residence, your share of the gain would be chargeable to capital gains tax.
She would be able to claim private residence relief against her share of the gain as she was living in the property.
The gain is £162,000.. if the property is owned 50:50 then your share of gain is £82,000. You say you helped her with the deposit and she has paid all the mortgage herself.
Please advise what the split was so to ascertain your share of the gain.