Frankly, it's okay to say no to things.

And women, especially, are just awful at saying no to obligations.

But guess what? You're an adult, and you absolutely can.

Really, you can.

I do it all the time (and yes, I'm a woman. so see? it's fine).

If it's not a priority for me, I say no.

It's a disservice to yourself and anyone you say yes to if you know you don't have time, or aren't committed, or frankly, just don't want to.  That's a perfectly valid reason to say no.

Will the person be mad or disappointed or whatever? Sure. Maybe. Maybe not. Who knows?

You still have the right to choose what you want.

Guilt is a terrible reason to say yes to anything.