Improv and Saying Yes

When I was in highschool, I took drama for several years with my favorite teacher. We did a lot of improv, which is acting without a script. Think of the tv show, Who's Line Is It Anyway? With improv, the actors can use games or suggestions from the audience about locations or themes to get the ball rolling. From there, they have to feed off each other and respond to each other's ques, words and timing. They never know what the other person is going to do or say next.
My teacher told us to never refuse an offer when doing improv. So, if my acting parnter said, "Wow! You ate that whole burrito. Isn't that going to give you really bad gas?" My response could be to fake a fart and say "Yah, it does it to me every time. Can I borrow some of your Tums? I know you have to carry them around since your surgery." To which my partner could respond by talking about the surgery (or better yet, pulling out their colostromy bag). The point is to make it as entertaining as possible for the audience, and usually humorous though sometimes it can be dramatic. It's only entertaining if the actors paint vivid pictures, with their words and actions, since there is no set and often no props.
If an actor is too embarrased to talk about farting, they might refuse the offer, and respond "Oh, no burritos don't do that to me." But that stops the story in it's tracks and the audience is disappointed.

So, here's the point of all that:
I've been trying to make my default answer to E, YES. I read somewhere recently about families that "say no to everything, and then the negotiations begin." I don't want to do that. If my default answer is YES, then it opens up a million possiblities of when and where and how she can do what she wants to do, while still being safe and respectful.
I really struggle with this though. And while I've been getting a little better, I still find that my YES isn't as enthusiastic as my NO. My YES is "hhhmmm, ok, I guess" or "sigh, sure, why not" instead of a joyful "I would love to help you explore the world!"
When she wants to do something she's making me an offer. She's giving me a chance to be a part of her world, help her explore, be her partner, watch her grow, and connect with her. When I say no, the show stops. The opportunity is lost. Too often, I say no because I'm busy with something else and I don't want to take the time. But then the negotiations begin, and after all the time I've spent explaining my no, figuring out how to justify it to myself (which is usually harder), listening to the tears, and trying to redirect her, I might as well have spent that time helping her do what she wanted to do. After all, that's where the learning and connection happens.
So, that's my newest challenge to myself- accept all offers, and see where it leads the story. This life is really one, big improv show.