Wife (Leah) does not do any farm work.

[Dron]

I have been married to Leah for a week in game, and I still have not seen her do any work on the farm even once. The only thing she sometimes does is give me coffee or a mushroom. Most of the time she stays in the house, or goes to work on her sculpture behind the house or goes for a stroll in the woods. I have maximum hearts with her and talk with her every morning. Its true that my crops do not require much watering as sprinklers cover most of them, but there are still over 10 tiles that need to be watered manually.

[Coffee Addict]

your wife/husband never actually work on the farm every morning they have a random chance to feed any barn/coop animals you have, repair any fences you have, water your crops, and fill your dog/cat bowl and randomly give you a gift

[Zoru-chan]

Are her hearts at max in the relations screen? Once you get married they actually gain 2 extra hearts they can have, putting the total to 12 hearts.

I don't know if they HAVE to be at 12 but I do know that Sebastian on my game helps repair fences, feed the animals (even though they are with autofeed), and waters my crops or the pet. How you will know that they are working/helped with the farm is when you wake up and they are standing outside right beside the door.

As Ryouma17 said, they also can give you gifts but they can give different types I think, depending on the spouse. They can give you a stardrop as well but will only occur once a game, meaning if you divorce and remarry you cannot get another stardrop.

[Violeta]

You marry for the starfruit, gifts, and rare chance they repair your fences for you.

[Dron]

Yeah I noticed the two extra hearts in relations after marriage, and I filled them too and check daily to make sure the relations are at max with wife. I don't really need the help, I just wanted to see it happen how the NPC goes watering the crops and feeding hay to animals in barns. Fixing fences is the one I care the least about really.

[Young Milf Kisser / Milf Enjoyer]

Theres also a mod that makes it so your wife/husband does ♥♥♥♥ for you