Hi lorna,
Welcome to the site, you will find lots of information on here, many members are pretty knowledgable about Turkey and we are a friendly bunch too
I have never stayed in Marmaris so I can't tell you too much about it or your hotel but I did live in turkey for a few years so i can tel you a bit about Turkey.
Firstly Turkey is a lovely country and the people are among the friendliest you will find. Your daughter and her friends will get a lot of attention so watch out for them, those Turkish men are real charmers - I should know, I married one
You will find Marmaris great for shopping, be prepared to haggle in the shops and markets and you will get some great bargains - clothes, shoes, jewellery, rugs, leather, pottery etc.
Are you going b&b, HB, AI? Turkish food is wonderful, I love it,; lots of different kinds of kebabs, vegetable dishes, Turksih pizza, salads and of course the very sweet desserts. Local beer, Efes is very good too, wine is not so good and very expensive as are any imported spirits. Local spirits are cheap but watch out for Raki as it can be lethal.
If you are prone to mosquito bites buy yourslef some lemon cologne, it is very ccoling and keeps the little pests away. You can also get a good repellent by Johnson's called Off, it is the best thing bother you a lot.
You will get a lot of friendly banter from the guys trying to get you to go in their restaurants, if you don't want to go in just say "no thank you" and go on your way, always works for me!
When you arrive at the airport you need to pay £10 for a tourist visa, you just get in the visa queue, get your stamp then go onto passport control, just follow the crowd and you will be fine.
I'm sure there is loads more I could tell you but I can't think at the moment, let me know if there is anything else you want to Know about and I will try to help. There are also a lot of people here who know about Marmaris can help too.
Have a great holiday
Kedi