Thanks for answering, good point about there maybe not being tax payable anyway!
So much comes down to your individual decision about risk.
OP, I had a similar sum 3 years ago - but given directly to me so no restriction how to use it. I've shared my decisions below, not because I think they're right for everyone, but because I thought it might help you to see someone else's thinking. If only to think 'oooooh, no way would I do that!' 
I put 2x £2880 into a junior pension. I "made" £1400 for her overnight due to the tax relief. For my £5760 payments, it is now worth £9000 after 3 years.
I wasn't sure about tying it up for 50 years (based on today's legislation). I also didn't like the uncertainty of not knowing how it would be treated by future legislation - what if state pension becomes means tested only, and she loses pound for pound based on what I saved? Also, I think that money earlier in life can pay dividends - like allowing an unpaid internship that catapults your career. It's just too long term for me. BUT the stats on 50 years of compound interest looked great... so I decided, worth a punt, but I won't add to it.
I also considered that she likely to have financial support for uni/house from both parents - so I'm not tying up the only bit of help she'll ever get. On this, I'm thinking - if it doesn't perform well, it's not so much to lose. If things are really hard financially before she's 55, then she's going to need money then too, probably. And even though she can't touch it, it might be enough for her to afford to opt out of her own pension payments for a year or two if she needs to find cash immediately.
Then £23K I put into a S&S ISA in my name - it has grown by £5K in 3 years. But the market has risen, and I picked something with a medium not low risk profile - again, because I'm not so worried that this will be the only extra help she ever has.
If it was...
I think I still would have gone medium to high (but still mainstream products) ISA on £20K, and put £10K in Premium Bonds. Just in case!
For the higher risk ISA, I would be thinking - you don't miss what you never had, and £10K is enough as an emergency cushion.