@Alex ************

Their must be a person at the place where you follow your internship that speaks Thai, let them call the Immigration Office and ask for the hand out with requirements.

The did manage to get all your documents together to apply for a Non Immigrant ED visa, it is not that hard.

@Alex ************

Talk with the school and the place where you follow your internship about extending your period of stay to continue the internship

@Alex ************

Yes, to apply for a tourist visa you need to go abroad and apply at an Thai Embassy.

@Alex ************

Single Entry visa has nothing to do with the requirements of extending the period of stay you got on entry with this visa based on following an education or internship.

Strange that you're enrolled in a 6 months internship and the school can only provide a 3 month stay, what is the reason why you can not extend?

Alternative is go to a neighbor country and apply for a Single Entry Tourist Visa which gives you 60 days on entry and can be extended once on basis of tourism with another 30 days

The Visa is a personal item, which means each of you has to meet the requirements on their own.

You might look into a Non Immigrant O or O-A for one of you where the person must meet the financial requirements and for the married partner a Non Immigrant O as depending on the partner without financial requirements.

As long as you enter before the valid until/enter before date mentioned on the visa, you get maximum 1 year of stay OR until the valid until date of your health insurance, which ever comes first.

@Tullio ******

That depends on what kind of stay she has, best is to ask that directly to your local Immigration Office.

Until 15 years of age, minors will not be financially fined, after 15 years until 18 year they will be financially fined but do not get blacklisted due to overstay.

As she is 17 years, she will be fined for overstay but not blacklisted.

You might try the Extension of Stay based on being unable to travel but with all restrictions getting lifted, make a plan B like short trip abroad.

The truth never hurts. But you might write down you are unable to travel due to covid contaminations world wide, or just I like to stay inside Thailand.