OK - that makes sense. If she's already used DSLRs, then I can see that mirrorless is a natural progression (at least in terms of ease of handling). I just wondered if she was asking for mirrorless because she'd read somewhere on t'internet that they were the best thing since sliced bread - clearly not the case with MrsC.
FWIW, all the various forums I read cite Sony as the go-to kit for mirrorless, but I suspect you may struggle with your budget (top-end Sony mirrorless are comfortably north of £3k - even the low-end stuff is over £500 for the body only)
Secondhand is your only option within budget - Wex Photo has quite a few pre-owned Sony bodies available -
https://www.wexphotovideo.com/used-..._Manufacturer=Sony&esp_category_pg=2As does Park Cameras
https://www.parkcameras.com/c/2503/used?p=1&q=2503&v=0&me=_ca&f=br:47|ca:2554&x=br:1|ca
No idea why the second link won't show as a hyperlink - copy & paste required into browser address bar
Probably worth reading a few reviews first though...