Cat keeps weeing on furniture

[Kaluki]

My cat is 3 years old.

Every now and then she will wee on the furniture - for no apparent reason. It doesn't smell that strong though, so I wonder if it is wee or some sort of spray and I have no idea why she does it. She goes outside for the toilet and can go out any time she wants so she wasn't trapped indoors.

The other thing is that she is always stealing food from the kitchen worktops. She is very skinny and I feed her dry biscuits and water so maybe I should put her on wet food to fill her up more?
Does anyone have any ideas on how to stop this? If she doesn't stop I will have to think about getting rid of her but God knows where I will send her - nobody will want a cat that wees everywhere but I am reaching the end of my tether. I wonder if keeping her outdoors is an option and not letting her in, but that seems a bit cruel.
Any advice greatly appreciated!!

cats male and female spray to mark thier territory i would suggest a light spray of lemon juice in water over your furniture as cats dont like the smell of lemon, i did this when i got my leather sofas and mine have never scratched them or weed on them,

might work for spraying aswell, is she neutered, has another cat come into her territory outside could be anxiety,

her being skinny i would try giving her some tinned food aswell, mine get a quarter of a tin in the morning and biscuits in the afternoon, if you try that and she dosent put on wheight might be worth taking her to the vets and getting her tested for hyperthyroidism as this makes them lose wheight but usually more common in older cats

Thanks for the lemon juice tip. I am getting new sofas soon so I will do that.
There is a big fat ginger cat who keeps picking on her so it could be stress - she is a bit highly strung!!
I will try the wet food too and biscuit combination too.
Flipping cat is more trouble than any of the dc!!!

I often babysit my MIL's male cat for a few weeks at a time and I have a boy too. At first they will both pee in certain places to mark their territories so after I clean it I put pepper over it and they don't pee in that place again, sometimes they choose a different place to do it though so I can spend ages walking around applying pepper. I either sprinkle it or for a stronger smell I make a little paste with water and spread it.
The lemon sounds good, better smell than the pepper so I might give that one a try too.

My cat is a lot older (16) but when he was weeing everywhere, skinny as anything yet eating us out of house & home, the vet diagnosed an overactive thyroid...It is not common in young cats though so it may be a stress/behavioural thing - have you tried a Feliway diffuser/spray? Bladder infection is another thought but my cats have never had that so am not sure exactly what signs to look for...

Another thought - my vet also suggested extra litter trays at the first sign of a change in weeing habits (my cats are not indoor cats but insist on using litter trays rather than going outside)

Hope things improve soon