If this was my application I definitely wouldn't try to skate over points of fact which the ECO will definitely question. This would be highly likely to get your girlfriends application denied.
First of all, the lack of work is sometimes an issue from what I have seen. All is not lost though as there are so many people in Thailand who work for cash. I would include something in her letter of intention to the ECO about her being let go from her most recent job due to COVID and as such you have been financially supporting her.
Secondly, in the same letter of intention I would make a strong point about her bond with her son & mother. Obviously she can't stay on in the UK working illegally as she has to be there to support her son and care for her mother... right?
As for the trips to the EX boyfriends country, there are two routes you could go down.
1.) you could tell a white lie that the trips were to visit friends or family.
2.) explain the fact that you broke up for 12 months and she met someone else.
Issue with option one: It's a lie and if they suspect so your girlfriend will have her application binned and possibly get banned for 10 years.
Issue with option two: Whilst perfectly normal in real life it may cause the ECO to question whether you are actually in a subsisting relationship.
It would be very important for you explain the situation properly and clearly. If you worded it well they would probably be understanding and her sticking within the guidelines of the visas would definitely be viewed as a positive.
Finally, the photos are now irrelevant. They used to accept pictures together as supporting evidence of a subsisting relationship. It all has to be done via the other documents you stated now.
Does your girlfriend own any land/house?
Does your girlfriend rent an apartment or house?
Does your girlfriend own anything of high value which can't easily be removed from Thailand?
Are there any other things that you can think of that may tie her financially or emotionally to Thailand?
If yes to any of the above it is also worth mentioning them in her letter.
I think it would also be prudent to state that whilst its her first trip to the UK, you think there may be future trips and would not want to jeopardise these by her overstaying.
Feel free to ask if you have any more questions. Everyone on here is pretty friendly!