J.P.
Last year my twins had to do this.... they each picked something that they liked for their 100 things.
My daughter found a bunch of gem stone type things from Dollar Tree and glued some to form a 1 and some gemstones to make a 0 and the remaining to make another 0. So... of course when she was done.... together it said 100. I suggest NOT gluing until she lays them out all 100 and then she'll know how many to use for the 1 - how many to use for the 0- and how many gemstones for the last 0.
My sone was crazy about Webkinz last year. So I went online and printed 100 small colorful photos of various webkinz and he cut them out and glued them in 10 rows of 10 to make 100. And... we talked about grouping about 10s.
Someone in the class glued 100 pieces of popcorn into a plastic popcorn container. (Cute) but I don't know if your daughter's has to be on a posterboard. Alot of people do cheerios or other cereal and dried macaronni. (Just so you don't do what so many others do.)