Accepting compliments is hard, especially physical ones if you're feeling awkward, and it doesn't get easier as you grow older.
I have never found it easy to accept compliments, it's almost as if I always assume people are somehow 'taking the p&ss'.
I learnt a valuable lesson from a teacher friend of mine when I was in my 20s. She was the specialist Art teacher in a primary school, and I was a class teacher. Much of her work was around talking to childen about their artwork, extending ideas, discussion etc, and she was always positive and complimentary in a non-patronising way. She was also very hot on getting children to accept compliments, and used to say very plainly, "I really think that's a beautiful drawing", and if the child just sort of shrugged in an embarrassed way, she'd say "No, look at me, I'm just saying what I honestly think, now I'll say it again, and I'd like you to look me in the face and say 'thank you'. You can smile if you like, but you don't have to, that's all". It was always said gently and with great sincerity,and it worked miraculously well. All the children gradually got over the shyness of discussing what they thought was good, brilliant, could be improved etc, because they had experience and practise of saying it and listening to honest praise.
Sorry, that was a ramble....the point I'm trying to make is, I agree with the others that you shouldn't stop saying how beautiful she is, but could you also talk about how people give compliments, and how it can make you feel emabrrassed, but explain that all she has to do is feel good about it, no ties, nothing in return, except perhaps to say 'thankyou'.
I'm not sure I've explained that very well. It's a tough one.