My sister did similar, but because her boyfriend at the time failed his A levels.
She deferred her uni place for a year and did another A level at a local college while working part time and saving some cash for uni.
Of course she broke up with said boyfriend immediately after they started uni anyway, but being a year older than her uni peers did her no harm (and there will be freshers of all ages on most degree courses anyway).
My sister actually met her husband because they were in the same halls - they’ve been married 20 years now, and might never have met if she’d gone to uni ‘on time’.
Agree with previous posters that it’s good to at least consider you DD plans for after uni - it might change, of course, but it’s not much effort to look up entry requirements for post graduate schemes or employers’ specifications for the kinds of roles she might be applying for.
She doesn’t have to make any decisions now though, and you’d be amazed at what’s currently on offer through clearing - far more prestigious courses than in previous years.
Last year my son was adamant that he wanted to go to his first choice uni, but he’s always been sketchy with exams (he’ll ace it on a good day, not even write his name on the paper on a bad day).
I refused to book any accommodation/make any arrangements based on his conditional offer, because I didn’t think he would get the grades (A,A,B). In the end, I was right, he got A,A,C, but the first choice uni offered him a place anyway, and he still managed to get everything arranged in time for the beginning of term.
This flying by the seat of one’s pants approach probably won’t suit everyone, but it was fine - so don’t panic too much, decisions can still be made after the exam results come in.