I teach first grade and can concur, that many of them just aren't developmentally ready to understand it. I hate that we have to expect them to do it in the first.
Definitely agree with the earlier poster that worksheets probably won't get her to understand the concept. She does need to work with things.
You can also get small Dixie cups and a bunch of beans. Give her a scoop of beans on a plate and have her count them in tens and ones. Tell her anything that is less than ten keep on her plate, and have her practice writing how many beans she has as just the number, and as _________tens and _________ones, also in the boxes just to get her used to how it might be presented on her tests and different worksheets. Also, reverse it. Give her a two digit number and have her show it to you in tens and ones using the beans and cups.
The popsicle sticks are also a good one. I would just get her to use lots of things so that she can see anything can be counted in groups of tens and ones.
Gosh. . .it is just such an abstract concept for the little ones.
A good website to go to and that is free is http://www.rainforestmaths.com/
They have tens and ones stuff for her to practice. Bookmark it, it is a very good math site that I use in my computer station.