Ok, here we go XD
 
Nebula can absorb magic from other ponies like her father, but she needs to do it trough physical contact. She’s still beginner at these so she usually use only unicorns since she can easily locate the best spot to drink up some magic (horn…you perverts).  
She could probably do that to another ponies or even species but…she’s just not familair with them and doesn’t know where to suck on.  
When she was a baby she used to do it to Celestia too. Now she is too embarassed to do it now. (“I’m not a baby!”)  
Royal Guards have a little circle of Nebulas victims. They usually meet at friday, serve tea and trying to move on with it. Feel free to join : D  
How long the magic will last depents of how often she’ll use it.  
Except magic she also likes to eat bananas, carrots, cucumbers, sasuages…I guess you already know the pattern.  
She and Riddle are fighting everyday. Celestia is still alive so I guess Riddle is winning.