She just wants something for around the lakes and hills where we live. It's mostly trails and some muddy bits. Might be worth having a look at Decathlon....there is one down the road from us....that's if it's open. She doesn't want to spend more than that loldo you need a mtb or just a hybrid? what kinda riding?
£350 is possibly a tall order for any semi-capable mtb. I wouldn't worry about women specific, just get the best components/frame possible for her size.
Voodoo from Halfords is usually regarded better than Carrera, but they now start at about £450 (unless you can find a sale after the lockdown).
Go Outdoor's Calibre range is also well regarded and it looks like there's one in the budget...
https://www.gooutdoors.co.uk/15904161/calibre-saw-mountain-bike-15904161/
Could also look at Decathlon, as they have a few cheaper options.
Yeah it seems like they are out of stock everywhere, might be worth a wait till shops start opening again and stock comes back in.https://www.merlincycles.com/ridley-blast-acera-mountain-bike-2019-118545.html isn't a bad deal for £350 but limited sizes... Lots of decent low budget bikes and equipment are out of stock everywhere and have been for some weeks!
The problem with really cheap bikes it you're basically buying a toy unless you spend a bit more, you certainly don't need to spend a fortune, but £300 for a hard tail MTB is really pushing it.
Some good suggestions above, also , this isn't too shabby for the price https://www.halfords.com/bikes/moun...n-mountain-bike---s-m-l-xl-frames-651472.html