A few things that haven't come up yet and are easier to sort out now than later.
If she ends up reapplying the year after A levels rather than deferring, ask the school now whether they support former students with UCAS applications and what their internal deadline is. Many do, but they tend to want it early in the autumn term, well before the January UCAS deadline, because they are busy with the new Year 13s. If the school won't help, someone who has left school can apply to UCAS independently and choose their own referee, who needs to know them in an academic or work capacity (a former teacher or an employer), not a family member. Getting a reference written this year, as a pp suggested, is sensible, but it will need updating with her actual grades.
If she applies for deferred entry, the year itself gets more attention than people expect. The new personal statement has a question about what you've done outside education to prepare and why it's useful, and for a deferred applicant the planned year is the natural answer. It doesn't need to be exotic. A job with some responsibility, a steady volunteering commitment, or saving towards first year all read perfectly well. What reads badly is "travelling" with nothing behind it.
Student finance is applied for in the spring before the course starts, so for a deferred place that's the spring of the gap year, not this year. The household income assessment uses a past tax year, so a year's delay shifts which year's income gets looked at. Worth knowing if anyone's income is likely to change.
Last thing, it's worth her keeping a UCAS option for 2027 on the list even if she's leaning towards a year off. Asking to defer a confirmed place after results day is usually a simple email, as AelinAG described, whereas getting a deferred offer changed to an earlier start depends entirely on whether the university has space.