On a Non -o multi entry you get stamped in for 90 days you then have to leave Thailand. You then re enter and get another 90 days. The last day you can enter and get your last 90 is the last date stated on the visa
she will get a visa if your answers are believable and backed up by documents such as your bank statements, copy of your passport. Chuck in her land/property deeds in her name… these can be translated on the day at VFS for a fee