How do I correctly feed my slightly overweight cat?

I have a 1.6 year old spayed female american shorthair. Shes an average sized cat and looked healthy until we had to move into my mom’s house in June where she owns an 8 year old spayed female American shorthair.

They get along good and the two of them were originally sharing one cereal sized bowl of food that would get refilled twice a day by my mom (I’m away at college the majority of the year). Except that it was clearly way too much food for the both of them and my cat began to eat—from what I can understand— because of possible resource guarding with there being another cat and only one food bowl. I started to see that my cat put on noticeable weight. When I returned for break I found she was 12.4lbs while my mom’s cat still maintained a healthy weight.

I ended up buying two Petlibro feeders that dispense dry purina cat chow for both cats three times a day for a total of 2/3 cups per day. I’ve seen a difference in her weight and she looks healthier, but in two weeks shes lost 0.6lbs (she weighs roughly 11.8lbs as of today).

She hasn’t been lethargic, she acts the same as usual, and there’s always food in the bowl. I just want to make sure I’m going about this correctly with good food amounts and in a safe way before I can schedule a vet appointment in May to get a professional’s opinion. Any advice would be greatly appreciated!