Transfer of apple watch

Hi my daughter was an iPhone user and had an Apple Watch paired to it.She changed to another brand and gave my wife the phone.My daughter cleared all her details and my wife set the phone up using her details.

A while later my daughter gave my wife her Apple Watch but it is no good to her as my daughter cannot remember her sign in details for her I cloud account so the watch cannot be paired.Does anyone have any advice as it seems a shame to waste a £200 watch?She has not kept the receipt.

Kind Regards

Tony.