There are a lot of good ideas in these posts!
One idea I can add is that you could first give her a just a few of them, keep them up on a high shelf, and explain that they're ponies for you two to share during only special pony playtime with Mom! That way, you can observe her with them and teach careful play by example-- and with direction-- until you're sure she knows all the gentle-play rules.
If you're unsure whether she'd definitely be careful-- even under supervision-- with the ones you have now and don't want damaged, you could buy a few less-than-minty ponies until you think she's ready for the ones in your current collection. Maybe guidance like, "Let's wash our hands first to keep our ponies pretty and clean!" and "Let's be gentle as we brush their manes!" would be good.
Perhaps the many you ponies you'd prefer not to display right now could go on "vacation" to storage and come back for occasional visits
Have fun with your little girl!! It's so great that you have her to share your love of ponies with!