I recently worked with a sensitivity reader and found it so helpful and insightful. Would it be helpful if I mentioned this in my query letter?
Dear Java Mama,
With sensitivity readers becoming more and more prevalent and important to the editing process, this is a good question.
Personally, I think you should mention any outside input you've had on your manuscript in your query. If you've used a sensitivity reader or a professional editor or any other respected service you should put that in your query. It shows a level of commitment to your craft and to ensuring the work you are presenting to a publisher or agent is the best it can be.
In the current climate where people are hasty and brutal in cancelling anyone or anything they perceive as being out of line, it may give comfort to an editor or agent to know that the book has been through a sensitivity reader if the writer is not of the nationality, sexuality or ethnicity of the characters portrayed.
Just remember that everyone comes to a story from their own perspective and experiences and even if you have used a sensitivity reader, they may not share the perspectives and experiences of other people in the group you are portraying. Which is why it's often helpful use more than one sensitivity reader or to try and find a diverse group of critique partners and/or beta readers.
It is also worth remembering that not all sensitivity readers are necessarily great at it and some may even have a bad reputation in the industry. Before mentioning you've used someone, ensure they are someone respected in the industry.
I understand that professional sensitivity readers and editors are expensive, so if you have expertise in a particular area, but know you need help in another, try and find writers you can partner with to help each other out. Maybe your ethnic background or sexual orientation can help another writer, while theirs can help you.
While I believe it is worth mentioning your sensitivity reader in your query, please don't count on this as being the thing that will put your query ahead of others. You still need a compelling query letter and a kick-ass manuscript.
Hope that's helpful, and good luck with your querying!