MY SIL is a nanny and I spoke to her recently about someone I know needing childminding etc and this is what she told me:
Childminders often have a few children at once in their house or a given venue, this means they have children brought to them by parents/guardians and can charge less as they have more income. Childminders can also be subsidised by local childcare schemes e,g, in my area they have a 'flying start' government scheme where they pay for people to train and then subsidise the childcare for parents going to that person.
Nannies go to your home and just look after your children. It is a specialised service and you usually have the same person for a number of years who will pick up your children form school, maybe clean for you (if they are so inclined) and cook food for your children in your home, maybe you'll take them on holiday with you or have them for weekends etc. It is more expensive as she explained because you alone are employing them and so they need the income all from you.
I hope you can see that your friend was actually just doing you a favour in explaining that your best bet is to get a childminder because it'll be so much cheaper and probably easier in the long run.
I'd email her back and thank her for explaining and for not just allowing you to hire her because it's in her best interests. She sounds like a nice person xx