Can my friend apply for a Non-O dependent visa in Thailand if she can't get it in Japan?

Hi all. Need advice (again) for my Japanese friend who is on a tourist visa.

She is going to apply for dependent Non-Immigrant O visa with her 3-year old son (who will apply for ED-visa) at Thai Consulate in Tokyo on Thursday.

She has all required documents except the "original" birth certificate. So now she only has a copy of it to to show the relationship between mother/son but not sure if it's enough. She will call Thai Consulate in Tokyo tomorrow and ask.

Here're the questions as of now;

1. If she can't get Non-O dependent visa in Japan and will fly back to Thailand next week, can she apply for Non-O visa at Immigration in Chaengwattana? If so, does she need to wait until her kid's first ED visa get extended to one year?

2. Should her son apply for ED visa first in Japan (in case it doesn't work for her)?

3. Both of their tourist visas will be valid till 15th April. The kid won't have a problem with overstay. But for my friend, how much does she need to pay for overstay? Does she need to do something about overstay before applying for a Non-O visa in Chaengwattana?

Any advice would be much appreciated!