She may grow a little bit in a month, and with shoes on, she may hit the 40 inch mark. Being said, if she is too short, they will not let her ride. Some CM's are going to be more strict than others. Example, last vacation dd measured 35 inches at her 3 year check up. (she is tiny). I was excited because I knew she could ride Barnestormer! The CM measured her as we entered, and she was right at the line, and he let us through. The CM loading the ride stopped us, and measured her, and let us through. She loved it, and since there was no line, we went to ride it again. This time there was a new CM at the front, who stopped, us, measured DD, and said "no go". I was very irritated, because dd was right at the line, and we just rode it. I said, "but we just got on it, we were measured twice, she is tall enough!" He said, "not on my watch". (I think he was on a power trip, and was super rude about the whole thing).
I would tell your dd that she is too short to ride those rides before you go. Have her wear her sneakers with thick soles, and first thing in the morning, see if she is tall enough, but keep reminding her that more than likely she can't ride.