There is not much "link" with the present. She studied there, but it's over and it doesn't have much bearings on the present. This really is a narration.
and studied at Oxfor University,…. – why they used past simple? It is an experience, isn’t it? I think it is
Because the period of time taken into consideration runs up to now. Now there's a link with the present.
but she has lived in the country for most of her life. – Why there is present perfect in here?
You could say that if she did it, say, once or twice. The corresponding question would be "has she ever written a book by hand?"
Could I say/write: She has written books by hand. ?
Again, if you say "she's been a teacher", it must have a strong link with the present. For instance, "she's been a teacher for two years" or "she's been a teacher, she must know the answer to this question!".
It is the same as in sentence: She is a teacher. –why don’t we use „She has been a teacher.“ ?
Yes, It looks fine to me.
Could we say: „She has always been a teacher.“ ?
- Is this correct? : I have heard that you had bought new clothes.
I would say "I have heard that you bought new clothes"
- Is this correct? : I have bought new clothes.
Yes, it can be correct, depending on context.
- Is this correct? : I have bought new clothes today.
- Is this correct? : I have once bought new clothes.
Looks wrong. Is there a tight link with the present?
- Is this correct? : I have several times bought new clothes
I suppose it can be right, eg. "I have bought (him) new clothes several times, but he keeps on wearing the same old pairs of jeans and dirty tee-shirts".
Am I correct?