'borrow' ? from whom? at what interest rate? etc. mystery to me. this is usual?
That is what margin trading is. Assuming you have $100, you can use it to borrow depending on the leverage you used. Assuming you have $100 and go for 3x, you will have $300 to trade, but there are an amount of money that you will pay after you finish trading with the money borrowed.
On all the exchanges that I gave used, you can be able to know the amount of coins you have on all your accounts on your exchange account, like main, trading, future and earning account. This can be done when you click on wallet or asset on the exchange, depending on the exchange you are using.
What is that all about? She couldn't have been tricked into buying on margin at all could she?
Which exchange is that? No exchange reputable exchange will let you unknowingly make use of margin trading, even you will have to transfer your asset from your spot or trading account into a margin account.