Umbilical Hernia's are totally common in our breed and about 70% or more Basenjis have them. So, your Vet is correct it is fine. Most people have them fixed when spay/neuter their Basenjis, otherwise unless there is a problem should be no worries.
I would suggest that you consider that there are better ways to introduce children to birthing then to have live puppies. There are books, videos, etc. Whelping a litter to introduce a family to breed is really not a good reason to breed a bitch. In breeding you should be looking to improve the breed as your motive, not as an educational tool.
Not sure why you would think that breeding would be good for her? Bitches do not need to be bred?
If you search the threads on this Forum, you will find lots of reason "not" to breed. And you should also learn about the breed, what testing for health concerns should be done before breeding (has your pups sire and dam been DNA tested for Fanconi?), judging your girl's conformation, temperament, and knowing that you should be responsible for any pups your bitch might have for their entire lifetime.