If she won't take the cash/check...maybe a gift card for something you know she would like. If she is someone who mentions "so and so massage place" or the nail place down the street....or if you know she likes a coffee shop, attempt to stop and grab her a coffee before work, or on the way to pick the kids up if you think she would appreciate it then (an iced coffee some people like). Or a gift card for a book store or if there is a preschool supply type place (Like Lakeshore Learning or maybe you can get an online certificate for a place like Discount School Supply so she can buy supplies for her daycare..paints and craft things, etc....I order online from there all the time!)
I am a provider..and always appreciated that a parent paid attention to me saying things like I wanted to try a certain restaurant, or I liked a certain one. Or that "Ahh..a peppermint hot chocolate suits me in any weather any time of day" (I said this once apparently! And on and off for about 2 years with one family, Mom would show up with one at drop off if they came a little later or at pick up..when she had the time...I loved the surprise!!!!).
I once was making sweet muffins from the recipe in my 1960's Betty Crocker cookbook (it was my mothers) and while I love the sentimental value and funny-ness of the "how to set a table" instructions in it...I mentioned to the Mom who saw us using it that "one day I will break down and get a modern one"....about 6 mos later when Christmas rolled around, that family had gotten me one! She paid attention and filed the comment away!! I loved that!
So just some thoughts....other ideas!