I'm not sure what a "thumb crib" is - but the device that each one of the moms who answered this question described is a "palate spreader" or "palate extender". I'm sure you already know that this device is used when the upper palate is narrower than, or doesn't line up with the lower jaw. It spreads the palate and allows room to then move the teeth around. It's like a plastic retainer that is cemented into the roof of the mouth.
I'm almost 49 years old, and when I was 9 - in third grade - I had one of these! That's how long they've been around. I don't think I wore it for very long - probably 2 or 3 months. We "cranked" it with the little key every morning and night, and by the time it was taken off, I could stick my little finger between my two front teeth (there was no space there before). Then they put on traditional "rail-road tracks" on both upper and lower teeth, that I only had to wear for 6 months! After that, I wore a retainer on top and bottom until all my permanent front teeth came in - and 40 years later, I still have VERY straight teeth.
I sucked my thumb, just like your daughter. My parents didn't try too hard to get me to stop, but boy, my grandmother did! I remember her trying everything. What a nightmare. But as soon as the palate spreader was installed, I stopped. It obviously didn't feel the same, and I just couldn't do it anymore. No trauma - not like what my grandmother did!
I don't have any idea of the cost - I know my parents paid a whopping $600 for the whole process back then (!) and I was somewhat of an experimental case - most docs waited until the kids were teenagers with most of their permanent teeth, but I didn't have to wear them for 4 or more years like they did. Less than a year, and i was done.