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earlier i saw my turtle opened her mouth, then a few minutes later i saw another one, awhile back she did a few popping sound but it stopped after a few days?

is it too late to take her to the vet?

No. It's never too late if there still alive.

No, now is an ideal time to take your turtle to the vets.
The sooner they can start an antibiotic course of treatment the better their chances are.
I took my one turtle Leo to the vets after I saw her swimming unevenly. I never saw gaping or reduced appetite, but I went anyways and got the antibiotics. She may never have developed a full blown RI but she did stop listing, and in retrospect I wouldn't have done anything differently.
Ezra, my rescue turtle had a much worse RI when I got him. He wasn't eating, wouldn't swim, and was gaping almost all the time. He too responded very well to the antibiotics.

The only thing you can do when your turtle has an RI is to get vet help. And, the sooner you do it the better. But, it certainly doesn't sound like your turtle has gone past the point of any help likely working.

I'd get an appointment ASAP.