Ok with further clarification - if baby is needing to be woken at 7:45 then breakfast at 8am is not unreasonable. Your OP did imply that the baby was already at screaming-with-hunger stage by 8.
But there's good reason why the standard definition of an au pair specifies that they shouldn't be in sole charge of children under 2. This girl is clearly not capable of properly looking after a baby of that age.
I think if I was you, with the details you've given so far, I would replan my own morning time (it shouldn't take 2 hours to get ready for work) in order to be able to scoop baby from bed into pram/carseat and leave the house with the baby at 7:45, giving the baby a banana to munch on en-route to the childminders, and let her have proper breakfast there. Then au pair just has to deal with 2 school-age ones which is more in line with her capabilities.
If you can't make something like that work, you need to replace her with someone who can. A nanny share with another family, who deliver their child/children to your house, could work out cheaper than this aupair+childminder combination.
You do seem to be paying effectively Nanny rates for aupair capabilities, but you can't make a person more capable by paying them more.