She’ll need to make sure that they can be driven directly from the tablet, without a headphone amp, with a 3.5mm jack. I think that these should be OK, used like new from Amazon at £111.33
I’ve owned the ATH-M40X and they were a very good well balanced headphone but that’s as cheap as I’ve gone. I did nearly recommend them but they break the £100 point.
I think either of those 2 headphones would be a solid buy.
IMO, no headphone under £100 is going to be spot on so go for a brand that has a decent rep and at this price point I like studio brands more as they tend to be built for long use so tend to be more comfortable. If I personally wanted something under £100 I would go IEM.