Maybe:
https://www.cyclingweekly.com/reviews/hybrid-bikes/btwin-triban-520-flat-bar
See also (more pics):
https://www.cyclechat.net/threads/btwin-triban-520-flat-bar-road-hybrid-bike-large.227178/ offered for sale by
@midlife
There are three limiting factors:
1)
Clearance between the fork blades (and you/she can measure that) (but
@Smudge makes a good point about the rear wheel clearances)
2) (Rim braked wheels) Getting the tyre
through the brakes when removing and installing the wheel. Any wider (than 25mm) and she can only get the wheel off (eg for cleaning) by letting the air out, and reinstalling flat before inflating (applies also to dealing with a puncture (reinstallation phase). The brake calipers look like 'long drop' so the other route is to accept that the brake cable clamp bolt will have to be released each time to allow the brakes to open out and let the tyre through. This is fine but two points: need to become competent at resetting the clamping accurately; and repetitive reclamping will result in the cable deteriorating relatively quickly and therefore require regular replacement.
3)
Rim width - a fair rule of thumb is no more than twice internal rim width. The images don't allow me to tell, but I suspect the OP wheel rim width is 15mm (622-15 may be in text on the rim), so beyond 32mm width tyres would be pushing it. Many will say it's no problem, but given the OP's stated objective concern is "balance and confidence" you don't want the tyres 'rolling around' as over-width tyres can do.
If I was the OP I'd change the tyres for 28s with some tread to grip off-road, tell the rider these are 'really good tyres and wider and grippier' so they are 'much more stable' and will offer her 'more balance', and let that installation of additional confidence do the rest. Because actually the
wider tyres will not make much difference to balance: maybe a little more grip, but it's marginal, except maybe uphill on rough forest trails.
