It's a difficult one. Ideally, I think I'd stick to the RC school for primary/preparatory years and then go for academic results in secondary education.
That way, all the important stepping stones of Catholicism (such as first Confession, first Holy Communion) have been covered, and your child has been given a firm foundation and grounding for years to come. The rest you can do at home with a certain degree of effort and commitment which you obviously have.
However, the impact on overall family happiness should not be underestimated and only you can judge that one. (Not easy I know but family harmony is as important as one's faith! Or, to put it another way, it's hard to focus on spiritual matters when everything at home is in chaos!)
Many family members of mine have faced or are facing this issue (fortunately not me as I live in mainland Europe where the best schools tend to be Catholic - phew!)
One example: my sister faced this issue with her ds. She opted to send him to an excellent CofE selective prep school and not the local Catholic primary which has poor academic standards. At the age of 11, her ds is now saying he wants to convert to the Cof E. His father is CofE so that could have happened anyway, but my sister (having promised at his baptism, with her dh's consent,to bring him up in the Catholic faith) finds it quite difficult to come to terms with.
Digression alert: it's an emotive issue too because sometimes the Catholic schools appear less "successful" because they are not selective. I was visiting my sister over Christmas last year and came across a rag-taggle band of 10 yr olds in the town square singing carols with their headmaster in the rain. They were scruffy and cold, wearing thin blazers. Two of the children had obvious mental disabilities but were joining in with gusto. Yes, you guessed it, they were from the local Catholic primary school and they were collecting money for charity and doing a good job despite the dodgy harmonies!! Their league table results are appalling of course but their main catchment area is from a very deprived area of town. Anyway, that's another issue ....
From my own experience, I went to a fantastic Catholic prep school but then my mother made what was in this instance the wrong choice in prefering faith over academic standards and sent me to an appalling RC convent school. (It had been good but had sunk to a dreadful state by the time I arrived.) At the age of 42, I'm still dealing with the negative effects of that experience. For that reason, for secondary education I'm afraid I would opt for academic results over faith every time.
Fortunately, neither of the schools you have in mind for your dd are appalling so whatever decision you make, it won't be a bad one. Neither will you be abandoning Catholicism totally if you send her to a non-Catholic school as you will continue to go to mass and follow Catholic traditions at home. However, family harmony allowing, I would go for the faith option up to age 11. Good luck and sorry for the rambling reply (I've got flu and am finding it hard to rally my thoughts in to succinct phrases!)
Hope you find a solution that works well for all of you!