She hasn't lost the bracelet, she has sold it, and the money hasn't been paid.
She should have received �25 plus �10 for the change she gave, making up the cheque of �35.
But �25 for the bracelet includes a �4 profit, so the in real terms she's lost �21 + �10. In terms of what she MIGHT have made, it's still �25 + �10 but that's like stock market players saying they've lost millions when share values drop -- they never had the money in the first place, only as a potential.
The �35 she borrowed isn't loss, since it's borrowed -- we are to assume that she will eventually pay it back. It's not really part of the problem, just a bluff to confuse.
BTW, know the one about the 3 guys who pay have a meal for �27, pay �10 each, etc etc and it turns out there's a missing pound? That one's even worse for getting mixed up!