Mat leave is to recover from the pregnancy/birth and look after the baby. It's not to become default cleaner/washer woman/shopper/chef/dogsbody.
some women want to 'do the house'
some women don't.
some women enjoy it.
some women don't.
some women might want to do something to keep up their qualifications/career, some might want to catch up on sleep they're not getting at night, or meet friends, go to baby classes.
women are, funnily enough, all different! This particular woman has said she wants to get a cleaner, she doesn't want to fall into becoming the house maid - easily done on mat leave. If they can afford it, why not?? Except the OP doesn't want a cleaner. Which I also understand. So there's going to have to be a compromise & only they know what that would be.
the op has said they don't want someone in all the rooms. Would they be ok with someone say cleaning the bathroom, doing the floors in the communal areas & the op doing the rest?
the DW can't make the OP accept having a cleaner & the OP can't make the DW do cleaning she doesn't want to do.
I understand both their views & my compromise would be different, but I'm the one home more & not wanting a cleaner.