Having fully comp DOES NOT automatically mean you can drive other cars. If your insurance certificate says words like this then you can:
"Policy holder may drive other vehicles not owned by the policy holder and not for hire or reward, with the owners permission, third party only"
If you do not have that on your insurance certificate then you cannot drive it on your insurance.
If she does the deal including deliery then the dealer would deliver it on trade plates. Dealers are desperate to sell cars so may well deliver it posibly for cost depends on how much she's spending I gues, worth a try.