The taxonomic situation I think is actually even more complicated than Geoff suggests. Blue-throated has been split by IOC (and therefore the Records Committee) into Chinese Blue (C. glaucicomans) and Blue-throated (C. rubeculoides with several subspecies rubeculoides, dialilaema and klossi). Chinese Blue is a long-distance migrant, from China to Malaysia, and is on Category B of the Hong Kong list. Blue-throated is supposedly resident.
Certain recent males in HK have shown some features of subspecies klossi of Blue-throated, including a paler orange breast and narrow extension of orange into the throat. In my opinion, the recent male(s?) at TPK also show these features. I think the RC are still investigating whether this could be caused by a captive diet, and whether there is any age-related variation. According to the literature, klossi is supposedly resident, occurring no closer than southern Vietnam. I don't know what females are like - there is a description in Robson but I can't find any photos.
So it may be necessary to consider three species in assessing these females: Hainan, Chinese and Blue-throated. I think these will be very difficult to assess away from the known ranges. I don't have much experience of female blue flycatchers, and these comments are based on literature not experience. As Geoff mentioned Chinese should show a paler throat, so this bird is probably not Chinese. This bird does seem to have a strong orange colour to the breast, which may suggest Blue-thoated, but that may also be related to age or light conditions. Robson suggests Blue-throated tends to show a stronger buffy eye-ring and paler lores; again this bird may fit. So, there are features suggesting Blue-throated but I'm not sure whether Hainan can be fully ruled out. Not Mugimaki though.
