If I understand you correctly, your partner is receiving. The serve is wide, and she calls the serve out. You think it was in. Is that the situation you are describing?
In that situation, I would not overrule my partner if the serve was anywhere close to being out. *My partner is looking down the line and has the better vantage point.* She may have seen space I was not in a position to see. I am not 100% sure she was wrong, so I will not overrule.
Let's change the facts now.
Your partner is receiving and you are standing on the service line and calling the service line. You see the serve hit the back of the service line, but your partner calls it out. What do you do?
In that case, I would overrule my partner (by telling her, "Uh oh. That caught the line, so we have to give them that point. Do you want me to keep calling the service line, or do you want to do it?").
Would you let her out call stand in those circumstances?