OP you can't be sure she has it. It's quite likely to be something other than Covid-19.
I know the advice is different in the UK than Ireland (where I am) as NHS advice is to treat as if you have Covid-19 and isolate. (In Ireland, you would seek advice and be tested, and we are in a period of self-isolation with different advice, thanks to Ireland proactively managing the situation, unlike, unfortunately, the UK)
So you are doing everything correctly but it can be any number of other viral illness, it's likely to be mild and self-limiting, take all reasonable precautions while not panicking.
It's awful to see the level of fear in the UK which I feel is directly linked to the poor leadership on the issue. The reality is still that for the majority it's a mild illness that self-resolves. The reason for concern is because it's new, we've no natural immunity, and for those with underlying conditions, it represents a threat.
I hope your little girl is well soon 💐