study, studies and studying - 'nauka' and 'studia'

In the Collins Polish-English/English-Polish dictionary, ISBN 83-7066-661-2, is the following entry:

studi/a (-ów) pl (nauka na uczelni) studies pl; (praca badawcza) research

When I used to communicate with young Polish people about to take their matura I used the word nauka when talking about their studies or their studying. A former liceum pupil, a very good friend now, is presently attending Politechnika Krakowska, studying Biomedical Engineering. When I write in Polish and ask her 'Jak ze studiów?' she tells me off and says I ought to write 'Jak z nauki?' She says I ought to use the word nauka when asking about her studies.

I am confused! In England, once pupils have reached the age of 15, we tend to call them students. But such pupils/students in Poland are referred to as uczniowie. In Poland, during language summer camps, I was told not to refer to them as studenci, this term being reserved for someone who is studying at university. This distinction I understand. But ...

Could someone please tell me when to use nauka, and when to use studia? At university in Poland, and among Polish university students are the words nauka and studia interchangeable or not?

Thanking in advance any person/all persons who reply to this request :-)

Yes.Student can say:
Ja się uczę.
Ja studiuję.
But highschool pupil/student can only say
Ja się uczę.

"nauka" if when you r studying to exam or something like that.. and "studia" is something called in english a College

Nauka and studia aren't interchangeable, the meanings are different.

Nauka or uczenie się is studying for a test, an exam.
Studia, studiowanie mean being a university student.
Nauka can mean also science and all the researches carried out by universities.

If you ask somebody Jak tam na studiach?, you not necessary mean studying, but rather just being a student - all the student life etc. (although it doesn't mean that this cannot include learning).

Jak tam z nauką? will be always about learning for e.g. exam.

Lenka is right that both high school (or even primary school) and university student can say ja się uczę and only university student can say ja studiuję, but it doesn't mean the same. If someone says ja studiuję he/she don't have to learn for an exam now, it only means that he/she is on a university.