Your daughter sounds like a brave, tenacious, hard working young woman, I can imagine you are very proud of her.
If you want some real life experience to share with her, I'm proof that education doesn't have to follow the linear path we expect of kids, GCSE's, A Levels, University etc. I started A Levels at 6th form college, but never took the exams, I knew I was going to fail them, and I didn't want to put myself through it. I left school at 18, just around exam season, and was lucky enough to eventually find an entry level job, where I could work my way up through the ranks. I do appreciate that these are much much harder to come by these days. What got me thorugh the door was my retail experience, and ability to deal with the general public, similar to your daughter.
Anyway, I went back to education when I was a bit older, in my 20's I did evening classes, and when I did do A Levels, I got a B, C and D. Much better than I might have done at 18. I recently came away with a degree from the Open University. I have a decent job, and am happily living my life. I don't think anyone has asked me for my A Level results in about 20 years.
There's no rule that says you have to do things in one prescribed way. She clearly has the tenacity and drive to get things done, so I would keep encouraging her, bolstering her confidence, and telling her how proud you are of her for giving it her best, and then make a pragmatic plan for what to do when she's finished sitting the exams, and for when the results come in. If she does better than expected, then fine, you can adjust, sameif she does worse. But you will have a plan and she will know what to expect and what to look forward to next.
And the very best of luck to her, I hope it goes as well as it possibly can for her.