You: 'OK cool, so how about we catch up after your dinner?'
Her: 'Sure, can I call you after dinner to tell you how I feel, and if I'm not too tired, we can get together?'
Agree to this and she's become a definite, and you're just an option... not a powerful position for you.
This is my take.
Many girls (and high value people) don't want to commit to a social option until the last minute, unless it's something huge. Especially young, hot girls who have more social options than they have time and energy and especially a potentially awkward thing like meeting up with a new guy (she's yet to discover how fully awesome he is).
When I'm presented with this situation I respond with a similar 'Oh hey that's cool, because I was going to do xyz. Let's just check in later and see how we feel at the time'.
At this stage I'll try and arrange something else, potentially with other girls or even just hanging out with a mate.
If I do arrange something else that is better, I'll do that and send her a very nice cancel text - 'Hey, a friend of mine is demanding I go out with her, I figured you wouldn't mind as you'd probably be tired. If you're not you're welcome to join us if you want'. If she complains I'd say something like 'Hey next time, if you can do a definite I'll be a definite' (with genuine politeness, naturally).
This will help train her to realise that unless she commits, I won't commit, and once you cancel on a girl 9 times out of 10 they start chasing even more ('wow, nobody cancels on me, he must have options'). It can be scary to say no to a girl like this. Isn't there some ancient wisdom out there, something along the lines of 'if you want something you must let it go free'?
If I haven't arranged something better, when the time comes I'll text or call 'Enjoy the dinner?'.
If she replies 'Great, but really tired. Raincheck?'
I'd reply 'Oh good, because I just bumped into an old friend and she's insisting on buying me a drink. I don't feel so bad now about having to cancel. Rest up and you'll have to tell me about it sometime'.
I'd then just do something else. There are plenty of other productive things I can do if I find myself with spare time.
Is it stupid game playing? Yes. But that's the unfortunate reality in my view for gaming certain girls.
Sometimes it's not about questioning or demanding certain standards of behaviour from people who are too young, inconsiderate or lazy to follow, it's about doing what's fair and effective.
I always give people the benefit of the doubt and try and make plans properly - but I'm not going to give my power away.
If a girl gives me a wishy washy 'Yeah, maybe', that's exactly what I'll give her in return (and follow through with).
If she gives me a solid commitment that's great and that's what I'll give her in return.