My wife tried to get her one today but they wouldn't give it without the father being there.

Is this normal?

I would guess this is a safe guard to ensure both guardians agree to the pp being issued, so that the wife is not planning on getting the child a pp and doing a bunk somewhere overseas, but usually if both guardians have signed the form this is ok

entirely normal.

But I believe there is a power of attorney form which can be signed.

My wife obtained a passport for her daughter without the father; but she did have the documents granting her full sole custody (or the Thai equivalent) from a Thai court.

Actually a very good law.

All I had to do was sign one paper and show my passport.

They were very surprised that she had a middle name.

We are planning to get Thai passport for my daughter, and facing same issue whereby my consent needs to be provided. Thankfully you can go to Thai embassy in your country and get the letter of consent which you can send to your wife and she can use it for application.