I don't think the embassy are issuing tourist visas at the moment. Under normal times you could get her a 10 year tourist visa with multiple entries to avoid having to make a new visa and all the paperwork each trip. It use to cost around 35,000 Bht.
Yes can show both. They will maybe take you to one side and put a stamp in the new passport to say visa is in your old one. I don't even bother going changing visa stamp and just carry both.