I am sure it is a truism that we worry most about the things we can least affect.
My head says you did not take her A levels, so you could not directly affect how she has done, my head also says that the papers are long since marked, moderated, checked so again nothing can be changed. The results will be in school/college by Wednesday so nothing can change, but because all of these things ARE beyond our control all we can do is wait and worry.
Perfectly understandable.
Chances are she will be fine but a plan B does no harm, including an open line of communications to her (I hope helpful and sympathetic) careers teacher/Sixth form tutor, and an awareness of alternative options - appeal to the university, Clearing etc being just two.
My 3 daughters all had disappointing results in ONE of their A levels and there was much wailing and soul searching. The eldest ended up at Manchester instead of Nottingham and could not have made a better choice! Great course, loved being in the North, wonderful friends and an excellent degree. The second did not let it deter her, carried on as planned took an extra year to get to where she wanted to be and has never looked back. The youngest rethought, reapplied for a totally different course, went travelling, worked to gain practical experience and ended up with one of the best degrees of her course.
Yes I wept with them but TBH if they had NOT had these setbacks I genuinely believe their lives would have been different and they would not be where they are now. They have done better and their lives have been richer precisely because of what happened.
Of course I can see how your DGD has set her sights on following in her brother and sister's footsteps and truly hope that all will be well. It is also natural that you worry, that's called love.