up to your neck vs up to her neck

up to your neck and up to her neck both are adjectives.

Word	Noun	Adjective	Verb	Adverb
up to your neck	No	Yes	No	No
up to her neck	No	Yes	No	No

As adjectives, up to your neck and up to her neck are synonyms defined as:

Other synonyms of up to your neck include neck-deep, up to his neck, up to my neck, up to our necks, up to their necks.

up to your neck (adjective)	up to her neck (adjective)
deeply involved	deeply involved