It was not represented well, but Celestia actually didn't dump "motherhood" on her. It's just that the comic was too small to make everything clear. The comic is from Twilight's perspective, a child, so everything is going to be the worst possible thing ever. It was also made clear Twilight would HELP Celestia, not do everything. I don't know from where exactly anymore, but it was made clear by it's creator that he didn't get enough comic space to represent everything correctly.