You may have to show PROOF of your DTV Visa to airline staff on check-in for your flight ✈️ to Thailand...even to the connecting airline staff. Or to the land border crossing entry Thai Immigration Officer.
Upon arrival into Thailand, show the DTV visa to the Thai Immigration Officer and look at the STAMP placed in your passport to be sure you are STAMPED in for 180 days.
A TM30 address registration will need to be filed with the Thai Immigration office.
Here's the common found requirements for the 30 days extension... Suggest you 🚫 NOT wait til her current expiration date ends as the extension is ADDED.
Are you staying in a hotel?
If you are, then the hotel should file with Thai Immigration the TM30 address registration form. Ask them for a screenshot of their filing.
... leave Thailand WITHOUT a re-entry permit and enter Thailand Visa EXEMPT entry...show PROOF of your flight departing Thailand within the 60 days you will be stamped in for on arrival...if questions from Thai Immigration Officer who greets you on arrival.