My cat will never let me touch her feet. It’s very hard to capture her to take to the vet. Is it absolutely necessary to trim nails if she uses her sisal post daily, and she is indoors only.
If her claws aren't giving you, or her, trouble, then I wouldn't call it necessary. It's generally a good idea to get cats into a habit of having their nails clipped at a young age, in case they don't keep on top of scratching when they get up in years (as this can cause claws ingrowing into the pad if left long enough). In your case, I'd leave her be, as long as you don't have any suspicion of her paws being painful.
I agree with Maurey
that it's not necessary to trim claws if they are giving you (or her) any problems. Scratching actually sharpens the claws rather than keeping them short. Back claws tend to get worn down just by the cat walking across a hard surface because they don't retract as fully as the front claws.
I have one cat who bites whenever I try to trim his claws. I end up putting a towel or blanket over his head like a hood and wrapping his body as tightly as I can, with just one foot sticking out. It can be done by one person but it's easier if you have a second person to hold her.