That seems like a good score Vijay for Bucks which I think takes the top 25%? However, a caveat, my ds has sat several mock exams now and they definitely vary in quality from the difficulty of the questions (in one local mock, over 20% got 90% plus which suggests there was not enough 'stretch' to separate the higher scoring candidates) and the peer group (ie; a cohort of 50 sitting in local mocks will give different results to say Sutton mocks, 1700 sitters). So all depends on the quality of the mock provider I think.
Bucks 11+ is designed to 'pass' the top 30% of the ability spectrum, I think - but the OP's DD is sitting the test for Berkshire, not Bucks
OP, did you mean to start your thread in 'Independent Schools'? Perhaps a kindly Mod will move it to 'Berkshire' for you.