Hi, I am from HK too and I did exactly the same to obtain A1 english test in UK before I came back HK. I took the test from Trinity College and they issued my certificate in a week time, while other providers issue certificate in a month.
I am in the process of application but ECO refused mine as they said my certificate from City and Guilds is not accepted, the point is mine is from Trinity College, have no clue why they said its from C & G. The only reason I can think of is on their HK provider list, there are only City and Guilds and Pearson in the list, so that's why they have mixed up.
One more tip, don't bother to put supporting documents in folder and box file, when you arrive in VAC Hong kong, the security will ask you to take them all out, which I haven't got clips and stapler so my documents were presented in messy way. So just clip them and maybe put a post- it on the top of the document.
If u need more information about the situation in Embassy, feel free to ask me. I am still anxiously waiting for the feedback from ECO. But I really don't want your wife to make the same mistake as I did, good luck
