Don't get the crown. Just have him fill it. I did this with my older son, mom. He had 4 molars that didn't have enough enamel - soft teeth, if you will. Sealants wouldn't even stick because there wasn't enough enamel. We had fillings done a few times. The fillings preserved these teeth until they fell out on their own.
Crowns for children are really not necessary at this point. They are a lot of work, they break, they aren't individually sized like adult crowns are, and they are very expensive.
Just get the filling done.
That said, is your child getting fluoride in her water? Check your municipality and see. If you have bottled water in the house, she isn't for sure. Fluoride supplements can make a big difference in whether or not she has a mouthful of fillings. If you didn't get fluroide when you were little, that could be part of the reason why you had so many cavities, along with the genetic disposition.
I have fillings and crowns and porcelain inlays galore in my mouth. No fluroide in the water when I was little. My parents too. My kids? I got the fluoride supplements and they don't have ANY cavities at all in any of their adult teeth. None. The only cavities my older son had were the soft teeth, which were thankfully replaced with healthy adult teeth. My younger son had one small cavity one time in a baby tooth that the doctor didn't even have to use novacaine to remove.
Make sure of your water and get her supplements if you don't have it. And don't bother with the crown.
Good luck!
Dawn