You can try to tease her mouth open by lightly running your fingertip from corner to front along her lips. If this doesn't work try tapping her on the top of her nose. If all else fails, put her on your chest and firmly hold her in place with one hand. Try to get a hold of her dewlap with the thumb and forefinger of the hand you have over/around her and gently pull down. IF you lean so that she is tipped belly up she will fight less and will allow you to pull her mouth open.
Once you have this accomplished you can put the food in her mouth with your free hand! Sounds tough but if you give it a try you will figure it out and find it isn't too tough. It's the best way to medicate or force feed as you can damage the mouth so easily by forcing it open by prying.
Good luck!
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Marcia - FroggieB Dragons
www.froggieb.com/MHDHome.html