i have leneth pregnate and hellhound appears in the secret room but when i interact with her it just asks if she wants to fight and she is not wearing a maid dress. Am i doing something wrong?

There is only a certain chance for her to appear in the maid uniform. You can use the teleport stone to the sleeping chamber to reset the variable and try again.

I have seen her in the secret room and had sex with a maid, afterwards i seen hellhound in a maid uniform.

That's what happened in my game, if it helps than you're welcome