Upvote:3
Your wife will need some document to show at the border crossing. Being the family member of an EU citizen will make getting the document much easier, especially if she plans to cross the border with you, but a document is still required. A normal UK tourist visa does not allow visits to the Schengen area, or vice versa. You can't expect the border guards to sort out marriage certificates, that's what visa officials are trained to do.
- You might try to apply from the UK, arguing that the trip is spontaneous and that an application from Thailand would be undue hardship. That brings the risk of being rejected because you really should have applied from Thailand.
- If you look at the Schengen visa application form, you will see that the family members of an EU citizen don't have to fill the most bothersome parts of the form. The fields 34 and 35 replace those fields marked by an asterisk.