Do NOT treat your children differently, no matter how you justify it to yourself.
I now families who did this - sent the 'brightest' child to private, or the 'weakest' one intellectually, or the boy over the girls, or the eldest but not the youngest, or vice versa, or the 'sporty' one... DO NOT treat your children differently by being seen to favour one over the other like this. It will affect both your relationship with them and their relationship with each other.
And as how to 'copy' a private education- the good news is you avoid the bad parts ( the overconfidence, arrogance, the lack of independence due to all the hand-holding, the pressures to perform, the taking privilege as the norm, not growing up with normal kids, just he posh ones) and focus on what your child needs.
The MOST important thing for a child's successful education is their parents engagement with it - and that doesn't mean pay for private school and chuck money at it, it means take an interest, read with them, encourage them to do homework, read, take them to the library, to museums, be interested in what they're interested in. Go and stand in the rain at 9am on a Sunday morning to watch them play a sport, and tell them how much you love watching them play!
If she struggles in a particular subject, you can look into extra support online or with a tutor. Learning an instrument is great for any child, and studying music helps with subjects like maths.
What sports does she like? Team sports are great for any kid, sign her up for football, hockey, basketball.
Is she prefer being on her own? Cricket is a good team sport for people who aren't really into teams. Or tennis?
Save the money and spend time taking your kids on holidays instead, having time together before they reach the age they won't want to bother with you anymore.