Which phrase should I use,"in her stead" or "instead of her"? I encounterted the both. Is there any difference in meaning?
"Instead of her" is the more common phrase, but it's also a matter of context. "Instead of her" can refer to a single other person, or multiple other people. "I'd rather spend a weekend with anybody, instead of her" or "I gave it to Lucy, instead of her." In either use, it has an implied exclusion - something happens to
B, but not
"In her stead" has a different connotation, more legal. For the definition of stead, Random House gives us:
the place of a person or thing as occupied by a successor or substitute
While "instead" does loop back to this definition, because it's derived from the same sources, "a stead" is something that a person can have. If you have proxy power for somebody, say as a shareholder in a company, you can "vote in her stead" while also casting your own vote. You're not "voting instead of her", because you're voting, too. It's inclusive -
A happens, and
B happens, just not by the person who is usually entitled to do