If she stays that way throughout the marriage, they should be fine.
On a more serious note, what scares me here is the lack of parental input. I would be terrified if my kids got married this way, but people do it, based on solid research and brief meetings. Many chassidim have a half hour meeting, and mazel tov. If there’s solid research here, and she’s just shy, this might not be any worse.
My question for you is, what input do you have? If none, I would say you can only do harm by voicing your qualms.