She should have the the obligatory CTPL insurance, it is needed to get the annual tax disk.
It is rather basic 3rd party liability cover with limits.
It applies to the bike with any legal rider. By legal I would say with a Thai driving licence.
You need to check that she does have a legitimate disc and insurance, rather that she is just 'saying' she has. The disc sticker shows the year (Thai calendar) and date, the month written in Thai.
If the police stop you, (and they will if you do not wear a helmet), 9/10 they just check your licence. For me that is normally the end of it as I have a Thai one. Sometimes they get to checking registration and copy of the book against the plates.
I have supplementary bike insurance giving extra liability cover and a higher bail bond amount which is required for farangs if you do get into problems.
It is a full year policy.
An insurance broker could tell you what is available. Getting your GF to look into it, or organise it is likely futile.
Perhaps call the AA insurance Office and speak to someone.
You could try an email but I have found that a difficult way to arrange things here..
Sorry this is not very helpful but I live here and hence do not worry about 2 week cover. When I was a tourist I always rented, that may be a better option for you. DK rental who posts here has discussed insurance before.