Okay...don't panic. Eggs can still hatch and chicks be healthy.
I had the same thing happen to me on about day 15-17??? I had 2 eggs explode. And yes, it makes a terrible smell and mess...and reminder to CANDLE those eggs earlier
...especially in warmer weather as they can go bad faster. My Welsummer-RIR mix simply sat on the mess; my Silkie very smartly rolled the stinky bad eggs out and away from the nest and the stink never touched her or her eggs (good for her!).
Of the messy Welsummer/RIR brood, I gently lifted and CAREFULLY pulled out soggy stinky bedding, and added more bedding that absorbed the rest of the gunk. Your hen has cleaned up the mess, so that's good. While it was not a super hatch for me (5 out of 14 eggs), I did still get some very nice healthy chicks.
And don't wait long for any unhatched eggs after 21 days. I was so tempted with the bad hatch to let them sit longer in case of late hatches, but with the warm weather and 2 explosions I pulled at day 22 after getting 5 chicks on days 20 and 21. It was a good thing. All the rest of the eggs were bad, bad, bad. You can tell because they smell, are very light weight, and thuddy slosh when you shake them. I put them in a garbage bag and cracked each one open to make sure I didn't inadvertently throw out a chick...but they were all explosive green disgusting goo.
My experience. Good luck.
Lady of McCamley