john, I posted your ? in the Trees forum, here's the response:

"Kousa is not a hybrid - though there are some hybrids of it and some of the native American dogwoods(C.florida, C.drummondii, etc.). But, if hers is a straight kousa, the seedlings will be typical of the species, and will be quite similar, in most regards, to the parent tree - floral show may be essentially the same - or it may be less or more showy - but she'll have to wait a number of years for these seedlings to grow through their juvenile period and attain sufficient maturity to begin flowering.
I have some seedling kousas that I grew from seed I collected, and they're probably 7 years old(if not more), with no evidence that they're inclined to begin flowering any time soon."

Here is a link that might be useful: Trees forum