The Fletch novels by Gregory Macdonald have an element of humor to them. Which, BTW, bears zero resemblance to the comedy found in the Chevy Chase movie versions.
I second the recommendation of The Gun Seller, and although it’s not a LOLLERSTORM, I also think A Heartbreaking Work of Staggering Genius by Dave Eggers is a welcome departure from heavy novels, by being a funny novel about someone who thinks they’re WORTHY of a heavy novel.
Fourthed. She might also enjoy Wodehouse’s Blandings novels.
True. I recently bought and read Life at Blandings, which has three Blandings novels. It was very funny, but I’m still partial to the Jeeves and Wooster novels.
Thanks for all the responses!
I see Jeeves and Wooster showing up quite a bit. I understand this is a series of books. Is there one she should read first, to familiarize herself with the characters, even though it may not be the best in the series? Or can she jump in anywhere?
Jeeves and Wooster are timeless and P.G.Wodehouse was a master of vocabulary, timing and background. 
As the BBC puts it:
“Though Wodehouse constantly poked fun at a wide range of targets - from the English class system and the ivory tower of academe to institutionalised religion - his satire was of the sweetest and gentlest variety possible. In fact, it is this studied innocence that arguably provides his detractors with their only real ammunition.
It is worth pointing out that, despite Wodehouse’s repeated intention only to write entertainment for entertainment’s sake, his work has long been revered for its richness of language. Any one of Wodehouse’s stories contains an astonishing variety of vocabulary, a capacity for literary allusion to satisfy the most intellectual of tastes, a wealth of witty dialogue, and an unsurpassed talent for simile. He has many fans in the loftiest reaches of literary study6, and was awarded an honorary doctorate from Oxford University in 1939.
It might also be mentioned that Wodehouse’s work has given inspiration to countless other writers and comedians including Stephen Fry, Hugh Laurie, Terry Pratchett and Douglas Adams.”
http://www.bbc.co.uk/dna/h2g2/A155891
Hugh Laurie and Stephen Fry really understood the characters, so there’s a TV series to watch* after you’ve read a few books. 
*though it’s region 2 (Europe)…
The early Jeeves and Wooster stuff are not novels; they are stories which are ordered in roughly chronological form, but which don’t have a unifying narrative arc. Since you said your wife doesn’t want a collection of stories, I recommend she jumps into the middle stuff. I can’t remember the name of the first actual Jeeves and Wooster novel; someone can help me out with it. But Bertie Wooster usually pauses to catch the reader up on the cast of characters and their relevance, in case he/she has not read the earlier volumes, so I don’t think you have to worry about her not understanding the later stuff in virtue of not having read the earlier stuff.
Three Men in a Boat by Jerome K. Jerome is timeless and hilarious. To Say Nothing of the Dog by Connie Willis is sci-fi, but an homage to the earlier book and also hilarious.
Carry On, Jeeves is a collection of short stories that starts with “Jeeves Takes Charge,” in which Bertie Wooster (suffering from what he calls a case of “the morning head” after a late-night dinner party the evening before) meets Jeeves. The latter cures the former’s troubles with a near-miraculous tonic (which makes its appearance several times in the J&W canon); based on the happy results, Bertie engages Jeeves’ services immediately.
That stated, it’s not at all necessary to read Carry On, Jeeves first, as Wodehouse does readers the service of making Jeeves & Wooster accessible from all points of entry. There are many secondary characters throughout the books, and Wodehouse describes each of them (through Bertie, the reader’s point of view) in each.
If you use Amazon’s “Search Inside” feature on Carry On, Jeeves (or any of the other Jeeves & Wooster books), you can read the first few pages and see if Wodehouse’s style may be to your friend’s liking.
The BBC series to which **Glee ** refers is available on Netflix, by the by.
I strongly, strongly recommend the novels of Douglas Coupland – not laugh-out-loud funny like Pterry Pratchett, but plenty absurd and hilarious in their own way, and totally mainstream, apart from a touch of magical realism here and there. Your wife will love them.
If she likes legal mysteries, there’s always Paul Levine’s “Solomon vs Lord” and its sequels. I also enjoyed Brian Haig’s novels. They may not be strictly comedy, but the main character/narrator, an army lawyer, doesn’t take himself, or much else very seriously. There are also William Bernhardt’s Ben Kincaid series (starting with Primary Justice)…again, this series isn’t really a strict comedy one, but the main character is so hapless and and idealistic, you just have to laugh.
Of course, these are all mystery novels, so if she doesn’t want people killed or abused, maybe she shouldn’t read them, after all.
Or you could read some of his work at Project Gutenberg, such as My Man Jeeves.
The Road To Gandolfo by Robert Ludlum.
And if you’re going to read the Fletch series by Gregory McDonald, you might as well read the Flynn series by the same author.
Ludlum went on to also write The Road to Omaha. with the same characters. They’re very un-Ludlumish books.
Anything by** Tom Robbins**…very fun…thought provoking and relevantly poignant.
tsfr
Did you know that Franz Kafka wrote his creepy, claustrophobic stories mainly to make his sister laugh? Give 'em another look.
Anything by Daniel Pinkwater.
Bill Fitzhugh has done some good stuff - pretty dark in places, though.
You could try Pest Control to start with…
Or you could simply go to the greatest of them all. Three Men In A Boat by Jerome K. Jerome. Read it, enjoy it, and along the way notice that he invented so many tropes of humorous writing that have been recycled by others ever since.
Fans of Hugh Laurie (Jeeves & Wooster, House) may like to know he has written a novel, The Gun Seller, that isn’t as well-known as it should be. It’s a genuine action adventure story based on someone getting inadvertently mixed up with a modern criminal gang. Although the story is told ‘straight’, the writing is excellent and very, very funny.
I’ll second that. I just started the ninth in the series, Hurricane Punch, and Serge is as wild and crazy as ever.