What she will have added to her student loan for the part year studied and what actually being enrolled for any part of that year will have done to her entitlement to further funding are separate issues.
From the government website, regarding the latter point:
If you changed course, stopped your studies or are repeating a year
If you stopped your course within the first year, you’ll get funding for the same course or a new course when you go back.
You might also get funding if you:
suspended your course or withdrew before it finished - and you’re going back to study any courseare repeating a year of your course at the same university, college, or institution.
If you stopped your studies for a personal reason(for example, you were ill or pregnant) you might get funding for all of your course - you should apply online with supporting evidence.
You can calculate the amount you will get by taking the total number of years of the course you are applying for and adding one year. Then take away the number of years you studied for. If you studied for part of a year you should count it as a whole year.
www.gov.uk/student-finance/who-qualifies
The overpayment of maintenance loan would normally be required to be repaid immediately, not added to the loan to be paid back later. If she actually received two instalments that year, that would imply that she was actually enrolled for the second term (and presumably noticed that this sum had been paid into her bank account...?).