Etiquette for Querying a Picture Book

I don't know if you have it, but I would go out and get a copy of Children's Writers and Artists yearbook.

In there it will give you a list of agents that handle PB's.

Most will give instruction as to what they will accept. Many accept the complete MS when it comes to PB's as a query letter could sometimes be longer than the actual book!

It will also give you an idea as to who the agents deal with and you can research to see if your style matches their successful authors.

Just to clarify, Jen.
If the agent is asking for a query letter then that is all she wants.
But I would check it out further. Many agents will accept PB mss instead of a query letter because they are so short.
The agent you are thinking of submitting to, may well handle other childrens work and the guidelines you have seen are referring to longer, fiction stories.