Does anyone know much about a parent claiming tax credits and using the 30 hours funding for their 3year old?

I have a mum who is a single parent claiming tax credits, including the childcare element. Her child will turn 3 soon so she was hoping to be entitled to the full 30 hours funding, split between me and nursery. He’s here for 36 hours a week. I’ve told her she needs to look into it carefully as I’ve heard some people saying it’s not worth claiming the additional 15 hours as tax credits will be stopped. I can’t seem to find any definite information on this.

Does anyone know how it works?

Would she lose all her tax credits if she claimed the 30 hours funding, or just the childcare element?
What happens during school holidays? Can she claim tax credits for the full childcare costs then when there’s no funding?
Could she claim 30hours funded and the other 6 through tax credits?

It all seems a bit unclear to me