TopsyandTim I cannot emphasise too strongly how important it is for someone becoming a sole trader to make sure they are set up properly with proper accounting for every penny she earns, making sure she pays her NI and sets aside money for income tax.
The fact that you did not realise that she would have to make contributions to NI, shows how unfamiliar you are with the complexities of being a self employed and it is so easy, with the best of intentions to find yourself with a burgeoning debt to the HMRC.
If you ever have had a cursory read of why someone, anyone, has gone bankrupt, or a small firm, and some bigger ones, has gone into liquidation 9 times in 10, their main creditor is HMRC.
I can see no reason, given your daughter's health problems and your support, why life will not be much easier for your daughter self employed - and without the stress, her health will probably improve as well,
There are sites online that can help her like this one www.money.co.uk/business/how-to-register-as-self-employed . Most self employed people I know have usually consulted an accountant or someone similar when they set up as self-employed and thereafter, pay an accountant once a year to deal with their tax return. There are expenses you can claim to set against tax and an accountant will know all about this