There is no law anywhere in the U.S. that prohibits realtors helping their buyer clients assist in pricing an offer. That is their job. What I suspect is your realtor is trying to protect his/her behind so if your offer is rejected, it's not your realtor's fault. What tricks these agents will pull so they don't look like the bad guy or better yet - protecting their rear ends.
What you CAN DO - if you want to stick with this agent, make sure you DEMAND that you look at ALL the sold listings in the neighborhood for similar homes + all homes under contract or pending + all active listed homes for sale. Make sure your agent gives you the property history for each home - even if it was sold. I know this takes some effort on your realtor's time but explain that if your realtor refuses to assist in pricing an offer, that you have the right to see all this paperwork.
Another option - speak with the Office Manager or Broker in Charge and have that person assign you to a different realtor. You are contracted with the brokerage - not the individual agent.