Absolutely agree with what has been said.
And utterly disagree with your trainer's advice to hold on to her until she relaxes... I know my adult dog wouldn't relax under those circumstances... I'm not suprised you got the reaction you did.
Look at the kitchen incident from her point of view.
Imagine you are exploring a foreign country - there have been a few locals around with you, but communication is difficult - they seem to like to give you some nickname, which you think you've figured out, and they like you to sit when they say another word, but a lot of the time they talk gibberish at you. You think you like them, but sometimes some of the smaller ones take you by suprise, or are suddenly there when you don't expect them to be, and then everyone seems really cross.
Anyway, you are exploring, and you find a fruit (chocolate, whatever....) grove - loads and loads of trees with really tasty fruits, many of which you've never tasted before... you select one to try. Suddenly one of the locals appears and starts saying something - you're sure you've heard the words before but you don't know what they mean, because you're too worried about keeping hold of this really yummy fruit... suddenly the local comes up and tries to grab it off you - well, you're not having that - there's plenty here for everyone, but you want YOUR prize... so you tell him "Oi, this is mine - back off" - but he doesn't listen (I guess he doesn't understand!) and picks up YOUR prize... well, you'd be mighty annoyed, wouldn't you!
And if his response to you telling him how annoyed you were was to confine you until you stopped complaining, you might stop briefly, but the second you got free, you'd still be mighty cross and would make sure he knew it...
If Jess hasn't yet learned "leave" there is no point asking her to do it in a high pressure situation... what you need to do, as Sarah says, is to prevent her getting access in the first place and, if she does get something, distract her from it, swap it etc.
Use a hands off approach - no physical confrontations or keeping hold of her until she "calms down" - she will want to please you, so give her the opportunity and guidance to make the right choices by using lures, rewards, distractions etc.
And let sleeping dogs lie!!! I wouldn't approach and fuss my adult dog when she was asleep... if she's asleep on me, that's different, as she knows I'm there and wouldn't be startled... otherwise I gently let her know I am there before making any kind of contact with her...
