You probably wanted to post this in Primary, not secondary really.
You can withdraw her, but only by keeping her at home for 2 weeks over the SATs week and the week after. Plus she will be doing all the build up and the stress. And SATs are a 'right of passage' and it may knock her self esteem even more if you don't show you have faith in her.
You are probably much better off working on the anxiety and helping her managing that. She will have 5 years of maths at secondary with regular assessments (DD has them every half term).
My DD was getting stressed by maths early in y6, as it doesn't come naturally to her. I explained that no one expected her to be able to answer all the questions and just to do her best. We sorted out what type of questions she could do, which were out of her reach and which were ones worth having a go at. When SATs came round she managed them fine in terms of stress.
She needs to be praised for having a go. That is more important to start with than getting the right answer.
Practice stuff she can do to build up confidence.
Use physical objects, eg chocolate bars would be good for halving 5.
Bring maths in to every day life, eg when cutting up a cake, or sorting coins.
Confidence is so key in maths. Now DD has started secondary her confidence is really improving as she is setted, and no longer with children who can get the right answer really quickly. She feels more capable, and hence she is.