agree with this from my recent personal experience. A few months ago, under ED visa, I went for a trip to Vietnam and I was strongly questioned at the back. I had the letter from school, the whole questioning was in Thai (I was studying Thai language) and they let me in after 15 minutes of questioning.
Please, note: I went for a quick trip to Vietnam over the Christmas. THREE days over a weekend, while all the schools in the country were closed for holidays. I mean, it was crystal clear that I wasn't missing any class because it was national holidays period... and still got questioned.
My advice: do NOT travel out of Thailand under an ED, not even for one day.
She has a Multi entry Tourist Visa. That visa is valid for entering the country during 6 months after getting it. Each time she enters the country during those 6 months she will be allowed 69 days permission of stay.
Visa will expire on May, but she can stay until June - or July if apply for a 30 days extension
Information is not (only) in your passport, it's in the immigration system. Getting a new passport doesn't delete the history of the person.
If you get a new one, the current visa/permission of stay will be transferred - but again, rest of the history is in their system.
It depends on the country but usually you cannot get a new passport until less than one year to expire date. But you can get a new one if the current one is lost/stolen, or if you run out of pages - but I think US will give you extra pages instead of a new passport.
Regarding time frame, I'd say 45 days is pretty tight, even my country which is very fast doing it needs 3-6 weeks... But best bet is to ask directly to your US consulate.
With a lot of history like yours, a cross for a 45 days exemption is pretty dangerous, they could reject you. To be covered, you must have an onwards flight, at least
*****
baht (or equivalent) in cash and proof of hotel reservation or equivalent, and do it through a land border in where if rejected you can enter again the country you've just left.
Spanish embassy stop the letter one or two years ago, now they put a stamp in the first page (reserved page, not for visas) stating the new passport comes from old one, with the old one's number.
I transferred my extension from old to new with that stamp without any issues ( at Chiang Mai Immigration)
Go to Immigration to transfer your current stamp to the new passport, as in the moment you get the new one the old one is voided. In addition, new passport implies a new number, usually you can change passports in airports (leave with one, enter with another) but better to play in the safe side for this matter. And, it's possible that you have some issues on leaving on a voided passport because where will the exit stamp go?
To transfer the stamp is a fast task. It took me like 25 minutes in Chiang Mai a couple of months ago, not sure about the queues in BKK but usually there are at least one desk specifically for this task.
By the way, it doesn't matter if your extension is near to finish or still have 11 months on it: this is a kind of a binary thing, it is over or it is not over. "Almost over" is not a state for this matter.
Regarding that bounce... on theory it's possible, but again you would play it safer if you stay overnight in Malaysia. Just leave the airport, go for some shopping in KL or some food in Penang depending or your flight, and come back the next day, not need to hurry up and make immigration officers to wonder (I'd spend at least one week, both KL and Penang are worth that time, but I don't know your circunstances)
If you're going to have a new contract on March maybe your company can write a letter/pre-contract for you just in case the immigration officer queries you about why you were working and now come back as a tourist - but don't show it unless required.