Do you need to have more than 20% home equity to borrow against for a home equity loan?

A friend just asked me to borrow money to pay her mortgage this month- she plans to take out a home equity loan to pay me back. She has only owned her house for two years, and I assume she would have only put 20% down. Will the bank allow her to borrow against that 20% or would it only be any appreciation in excess.