TBH, I’ve sold lots of bikes to 5’2″ women and none of them had issues with standard brake/gear levers on an MTB (road STI’s can be a problem).
Wheel size; I wouldn’t go near 26″ these days. 650B will be fine.
Frame; rack fittings are a lot less common now. Many of the “euro” brands will have them though – Cube being an example. I’d also go for aluminium and not steel as smaller people appreciate the weight saving.
It would be worth looking around to see what complete builds you could find as you’ll often get a better deal that way.
Edit: £60 for that Cube frame linked above. Snap it up!!!