I think she'd be a nanny. you'd need to employ her properly and give her a contract, deduct and pay to the IR her tax and NI and all the other aspects of being an employer. You couldn't, as far as i know, use her on the same basis as a childminder (i.e. she can't be self-employed).
A childminder works in her own home, sets her own fees, policies, daily routine etc.
Ofsted say you don't need to register as a childminder if you
look after the child wholly or mainly in the childs own home
look after children for two sets of parents wholly or mainly in the home of either or both sets of parents.
"Mother's help" implies household duties as well as caring for child
Sounds more like a nanny (employer/employee relationship) to me.
lunavix - think the home childcarers were/are phased out, I never could see the difference between that role and a nanny.
lunavix, Home Childcarers are now phased out. It has been replaced by Approved Childcarers.
An Approved Childcarer cares for children in the child's home. Approval is via the Childcare Approval Scheme which does not do as much checks as would be done on a Registered Childminder, but does at least make sure the person has an Enhanced CRB Disclosure and First Aid training.
Nannies are being encouraged to join the scheme as parents using an Approved Childcarer can get some tax benefits by using Childcare Vouchers.
With regard to this specific situation, any care at your home is unregulated. In England, care provided at someone else's home (Childminder) or a childcare establishment (Nursery, Pre-School, Holiday-Club) is regulated by Ofsted, as long as care is proivided for 2+ hours - any care provider working less than 2 hours, is unregulated.
As mentioned by others, if you employ the ex-Childminder to care for your child, at your home, they would be classed as a Nanny for tax purposes - so you would need to register as an employer.