For someone who loves Peter Wimsey, Paul Temple and the Toff...

I'm a fan of the authors mentioned and would thoroughly recommend the books of Josephine Tey. She's a very good writer, though a bit dated (having written in the early part of the last century). Her detective books (The Shining Sands, The Man in the Queue, A Shilling for Candles etc) all feature the same detective and I enjoyed them hugely. Hope this helps!

I prefer Hamish MacBeth to Agatha Raisin.

Georgette Heyer wrote several mysteries, some were extremely silly (the earliest ones) but a couple were very good.

She may enjoy

Ngaio Marsh - Roderick Alleyn
Margery Allingham - Albert Campion
Elizabeth Peters - Amelia Peabody (?)

Patricia Highsmith?
Nancy Spain wrote a couple murder mysteries - Poison for Teacher

Seconding Josephine Tey.

I would suggest the Carola Dunn Daisy Dalrymple series of books.
Ann Granger - Mitchell and Markby series (not set in the past but god and not violent - traditional whodunnits
Also Ann Grangers Lizzie Martin books -Victorian whodunnits.

I second the ones others have recommended - esp. Josephine Tey she's a great writer - I'd recommend The Franchise Affair and Brat Farrar.

Also - a really excellent and very well written mystery/crime series is the Shardlake books by C J Sansom - set in tudor times.

Edmund Crispin is quite a good old writer of traditonal puzzle whodunnits (think he was writing in the thirties/forties?)

Oh and Patricia Wentworth's Miss Silver books (roughly comparable to Miss Marple type whodunnits)

Just thought (sorry I keep remembering something after I've clicked post!) if she goes for the Shardlake books its probably a good idea (though not absolutely essential) to read them in order the first is called 'Dissolution'.

P D James is another writer in the more traditional style.

Also - Nicholas Blake (detective story writing pseudonym of the poet Cecil Day Lewis) is another one she might enjoy - along the same lines as DL Sayers et al.

For a complete diversion, try Jasper Fforde

Also seconding Margery Allingham and (to a slightly lesser extent) Ngaio Marsh

What about DM Greenwood? Churchy mysteries, about 15-20 years old now. Well written, not graphically gory, lovely acid observation of church politics. The 'tec is a woman in deacon's orders-very upper class and horsy, which I always enjoy (love Josephine Tey for similar reasons).

Fear DMG may be out of print though. I got mine through AbeBooks.

Yy Josephine tey. And there's a series by Nicola Upson where Tey is the detective.

An Unsuitable Job for a Woman might suit too (PD James)

Inspector Morse books?

Michael Innes (eg Death at the President's Lodging, Appleby's End) - I would say these would definitely appeal

And what about Dornford Yates - the Chandos books (disclaimer, I haven't read them for years, but I remember them being amusing)