I would endorse what Herman says here. DD also did early GCSE with A* in Year 10. She and her top set colleagues found the FSMQ really challenging and downright hard at times, and 2 decided not to sit it. DD plugged on though, and like Herman's DS, DD was pretty amazed to get an A. She is now 2 weeks into an AS Maths course and says the FSMQ has helped 'masses' - she feels really confident in a subject which was probably her weakest at the start of secondary school, and is really enjoying it now. While I am sure there are others who didn't do it and feel just as comfortable, for my DD this has been a really good thing to have done, if only for her own confidence. So though I can't advise your DD Asha, my hunch is to say go with it - you and she might be surprised.
ETA - well done to your DD solimum and good luck to you when she goes away today.