Pick a mall close to her incall and get a general gift card for the whole mall. That gives her the option to pick from multiple stores. Or a prepaid visa/MasterCard from shoppers drug mart. Just something she can spend anywhere.
Then I would get a thoughtful "thinking if you" type card or even a blank one, where you can write a little note, expressing your apprecaition for her and explaining you would have loved the chance to shop directly for what she may want and make it a proper gift, you respect her and her privacy enough to never intrude. So this was the happy comprise you came up with.
She will appreacite both gestures. The thought of the gift and the respect of her in the process.