I'm worried about my baby

I have a 9yr old cat Reba, she is my baby. Well my problem is about a couple of months ago we got all our animals flea collars. About a week after I noticed reba started losing fur in patches on her ear and on her face, she also was losing weight "She's always been alittle chunky " well we thought she was just getting older but it just got worse. So one night we thought to take the collar off, the fur grew back but in the past weeks she hasn't gained any weight. I want to take her to the vet but I'm not sure if I should wait or not. Any advice would help Thanks.

I would not wait.
Flea collars and flea products that come from the stores are just dangerous.
Get her checked out, and on a monthly flea preventative from your vet.

time to see a dr

Take the flea collars off right now (they don't work anyway - the stuff you get from the vet is a million times better) and make an appointment with the vet.

While she's at the vet, mention the weight loss and ask about having a senior panel of blood work. When older kitties lose weight, it can be a sign of hyperthyroidism, which is very treatable, especially when caught early. Even if the blood work comes back normal, you'll have an idea of what her baseline is for the future.

Thank you for all the advice, I will be making a appt this coming monday morning.