Learn French: Elle s'y prend très bien avec le feu.

This is a great example of an idiomatic pronominal verb! While prendre means "to take", the fixed phrase s'y prendre means "to go about doing something", "to handle a situation", or "to manage". The meaning shifts completely when you combine it with the reflexive pronoun se and the pronoun y.

Does the y in s'y prend replace a specific phrase here, like a location?

No, in this case, the y is just a permanent, built-in part of the idiom s'y prendre. It doesn't replace a previously mentioned place or a phrase starting with à, which is how you normally use the pronoun y.

Why do we use avec (with) instead of another preposition after s'y prend?

When you want to specify what or who you are dealing with, this expression requires avec. For example, you could also say Il s'y prend mal avec les enfants (He handles kids badly). If you wanted to describe an action instead of a noun, you would use pour followed by an infinitive, like s'y prendre pour allumer le feu (to go about lighting the fire).

Could I put the adverb at the end and say: Elle s'y prend avec le feu très bien?