When I defeated the Ender Dragon I expected to receive loads of EXP as I saw on YouTube when people defeated the Dragon. However, when I defeated it I got no EXP. I thought that maybe it was a new update. So I didn't really think anything of it. A few days after I defeated the Dragon my sister wanted to join my world (she played on an iPad), so I let her join. When she joined she had 68 EXP levels and 10 dirt blocks. This was her first time joining my world. I was incredibly confused as to what was going on. The only reason I could come up with is that the game glitched and gave her my Ender Dragon EXP levels. And the reason why she had the dirt blocks is that they fell through the portal. I was trying to cover it up so that the Egg didn't fall in the portal. And when I was deleting the dirt blocks some fell in the portal. I would really like to know what is going on. And I would like my EXP for defeating the Dragon. It would be really appreciated if you could help.
Related issues
Comments

The XP must've gone through the portal and appeared in the world spawn, just like the dirt.
Thank you for your report!
We're tracking this issue in MCPE-58715, so this ticket is being resolved and linked as a duplicate.
That ticket has already been resolved as Fixed. The fix is already included in the latest version of the game, you can check the Fix Version/s field in that ticket to learn more. The issue is that the XP orbs would fall through the end portal and land at world spawn, so when your sister joined she got all of the XP.
If you haven't already, you might like to make use of the search feature to see if the issue has already been mentioned.
Quick Links:
📓 Issue Guidelines – 💬 Community Support – 📧 Mojang Support – ✍️ Feedback and Suggestions – 📖 Game Wiki