Putting my fat cat on a diet!

Hello everyone!

I have some questions about diet, but before I start...

My gorgeous Lily got back from the vets just before after having her tooth pulled out and all is well!
The vet said I need to give her antibiotics, watch her mouth for swelling, and he showed me that mother of a tooth that came out of her mouth!
Although, he also said that I might need to coax her into eating....... good one! The second she got out of her cage she drunkenly stumbled over to her empty bowl demanding some food!

She looks very drowsy and to be honest I think the only reason she's awake right now is because she's eating. She's even eating wet food, which she normally hates. She's stumbling around and tripping over herself... it's very cute.

Now for my query ...
In all my life of having cats, I've always had healthy cats. Far from skinny, but never overweight. I've always fed one serving of wet food per night, and free fed Optimum (used to feed Science Diet) all day and night. All my cats seemed to be able to monitor their own diet.
Lily's my new cat, and she's different.
Firstly, she won't eat wet food... honestly, her eating the gravy off some meat right now (because she can't eat dry because she got her tooth pulled) is the best I've ever gotten her to do. She won't even eat smelly human tuna!
She smells it and licks it, but usually it's left mostly uneaten.
So she just gets free fed on Optimum all day and night, and she doesn't seem to be able to control it like Memphis can. Memphis only eats when he's hungry... but Lily eats like it's going out of style!
I'm thinking I'll have to put out a certain amount of dry each morning, but how do I stop Memphis from eating Lily's food? It's just really hard to monitor...
Also, would wet food be better for her diet-wise?
I will shortly be changing her dry diet to a special dental food because of her tooth that the vet recommended... but for the life of me I can't remember it. It'd be Australian, and they sold it at the vets. It was 2 letters (the name of it) but I can't remember!
She does love to play a lot and I have been getting her moving more than usual lately.
Anyone else have any other tips for slimming down this fatty? (or as the vet says "a little "too" healthy!")

TIA everyone!

oh and apologies for long post... gosh I babble

I would start by switching from free feeding to meal feeding the dry food. While wet food is certainly something to consider, I think it would be better for her to adjust to getting food only at certain times first. The dry food you mentioned is probably Hill's/Science Diet t/d. While the ingredients aren't great, it is one of only a few foods to receive the Veterinary Oral Health Council seal.

If you switch to feeding meals instead of leaving food out all day, both cats will have to learn to adapt to eating when food is available--then you won't have to worry about them eating each other's food since you can feed them in separate rooms if they start looking at each other's food bowls.

I think free feeding is ok for a cat that is not greedy but for a greedy one you may consider grain free foods. I used to feed wet that had some grain in it and they were hungrier faster. If she is addicted to a certain food I would think about changing it. It could help her slow down some.

My fat 4 year old fixed boy weighs 22 lbs i was told when we were at the vet the other day , which is up by 2 lbs in a year. he is an indoor only cat and i feed him only an 8 oz cup of food a day that he can eat all through out the day. the vet said to be carefull trying to help him lose weigh as it can be bad if he lose's more then a half a pound a month , as it can cause liver issues. Wet food is good and you can also mix an extra bit of water into the wet food as my vet told me to do, as not only with the wet foods moisture help put a little more water into his systen, but will also help prevent crystals and other urianary issues. My vet said too that a bit of water mixed in with wet food may help too by making the cat feel fuller, so he isn't as hungry all the time. i am trying that out and hopefully my boy can slim down a few lbs before we go back to the vet next year.