Giant avail? Not sure which retailers she can use but
Evans have as good a range as any, except giant
Advantage of giant is their own decent mudguards which are required for a commuter.
If she's not especially petite, then she'll have more choice looking at men's/unisex ranges too
£500 is quite a low budget especially if restricted to certain retailers. Boardman have a wsd bike for £500 I think.
Decathlon Tribans offer excellent vfm, 500 with carbon fork and sora under £500. May require a stem, bar, saddle change though