What is this "senior classification stage"????
What you are doing is teaching your puppy that what you give her you will be taking away
...a sure fired way of her being aggressive around food.
Please do some reading here...do a search on "puppy food aggression"...read all of the "stickies" in the Puppy Development forum.
Instead of this "alpha" business....try to work as a team...you are the leader...and the puppy is the student.
Play the trade game....she has something good...you show her something even better (bit of chicken or cheese) and say "drop it" or "out" or whatever you want to use...and trade. Then give her the prize back. Keep doing this for weeks..and she will soon drop the item just from the command.
Have you got her enrolled in Puppy Kindergarten classes yet? It sounds like you are making some mistakes, and you really need to get in touch with a trainer.
There is also so much good information here....read and learn.
Gina