
Agree with denese, as long as her diet is good, milk will come through. After a section, it does sometimes take a while longer for things to settle. Just keep putting the little girl on to the back teats, and encourage the suckling to ensure further milk production.
As to only 2 teats producing, I think this is normal in small litters. One of my breeds has 1-3 pups and I often find that milk isn't produced further up the teats. Remember that more milk will be produced as pup demands more, and it's early days yet. Make sure your bitch is drinking plenty, she sounds to be doing fine looking after her little girl, I think your vet will be happy enough with her. Try not to worry too much, you don't want to pass on your anxiety to your new mum.
Good luck :-)