Looking for some help for a bike for my mum

Hiya, I'm looking for a women's hybrid bike for my Mum and have no idea where to start.. There seems to be a ton out there, but I'm looking for one with a relatively good gear range, not entry level components preferably, and has to be quite light as she has the beginnings of arthritis in her thumb. Looking around the £400-500 range. She isn't bothered about the frame shape being the dutch or more mtb style, but would like a low stepover. She would be doing some road riding, but it'll be mainly for country roads and wee paths and things when she's away in her campervan. Does anyone have any recommendations? Any help would be appreciated. Thanks in advance!

Which hand is the thumb issue ?

Left hand shifters tend to be for front mech on chainset.
Right hand shifters tend to be for rear mech gear changes.

The higher end groupset shifters tend to have sealed bearings in the mech and have a lighter feel than the cheaper bushed units.
Gripshift may be an option.

In other words.... shifters, should be viable to upgrade a unit for less effort at the hand.

Thanks very much for getting in touch, it's her right hand that is causing the issue unfortunately, holding and pushing with it can cause her some pain. That's definitely helped me narrow things down, thank you!

Moulton? Low step through frame. SRAM kickback gears so avoids shifter issues.
Out of your budget new, if you can find a used one...

Ooh, never come across them before, the engineering it must have taken to get that frame shape! Sorry, I should have mentioned, she goes away in the campervan too so would need larger wheels and clearance for larger tyres and stuff for wee trails and things, I'll edit the original post. Thanks very much though!