A parcel from the U.K. to anywhere abroad must have a Customs Declaration on it. This is a label you list the goods on it with the price of each item and then the total cost and you sign and date it. If you put less than the value it is an offence, however, a lot of people do it, but if the parcel is lost or damaged you would not get the full value of your goods. Also customs have the right to open any parcel they want to. Up to 2 kilos it can be insured and sent by Royal Mail if it meets their size requirement, it will be measured, over 2 kilos it must be Parcel Force. Any breakables will not be covered by parcel force, a Parcel Force customs label is a lot bigger than the Royal Mail customs label. I would advise you tell your friend to pack and weight the parcel then measure it and then go and get a couple of the relevant labels. The P.O. will be happy to give them to her as it saves them time at the counters. They will also tell her what the parcel will cost if she gives them the measurements. She should fill the label in and take it to the P.O. with the parcel.
If it is send by Royal Mail or Parcel Force it should be the Turkish P.O. that handle it.
I am sure an ex-pat will be along with information about that.
The P.O. is not cheap to a send parcel, she may be better to use a carrier. The last parcel I sent to Australia which was over 2 kilos and sent by Parcel Force cost me £70.00 to send.