My two cents worth and take it with a grain of salt even though it comes from a wealth of experience because every lady and every situation is unique.

Ask her out to do something that is an experience or to create a memory. Not just a dinner date.
Something where she can enjoy your company and enjoy herself, so she remembers it fondly.
Even better show you care by doing a heartfelt gesture. Can be as small as a single rose or bringing her lunch to your next session and letting her eat it on your time.
How she reacts will give you a lot of valuable insight in to her character and what she is looking for.