Question about US Embassy in Warsaw. Going to interview with my wife's mom?

I am a US citizen, I have never been there and we are going to try once again for my wife's mom to get a visa to come here to visit us in the US. I will be there when she has interview. Will I be allowed to go in to the interview with her?

I doubt that. However, why don't you call the embassy and ask them, this could be doable.

An excellent idea. I'd also ask them if there is anything at all that can be done to increase the chances of the mother-in-law getting a visa (for example, it used to be possible to put down a bond which would be forfeit if the person did a runner).