Hi. Hang it there. Sounds like you have tried tons of stuff, but I thought I would throw out a few ideas just in case. Forgive me if you have tried all this, just trying to help.
-Soups? My 20 month old will sometimes eat things in a soup that she rejects if I just offer it alone. You could add beans to a soup easily.
-Puree some beans and try it on her toast or in her mac & ch (though I have read that such attempts to hide food can backfire and cause rejection of the liked food too...maybe just try a bit at first).
-Beans with cheese melted over it? Cheese does make everything yummier. Any kind -navy beans, black beans, kidney beans - I buy canned beans with no sodium (Eden brand).
-What about dips? Would she dip her toast into a cheesy bean dip?
-Tofu? Cut into cubes in a broth? Or just warmed up and as finger food?
-Muffins using some kind of grain flour that's a bit higher in protein than white flour? Plus baking usually involves a couple of eggs, which can't hurt your cause.
GOOD LUCK!
P.S.: Vegetarians do not get protein only from dairy - other protein sources include nuts, grains, beans beans so many types of beans, tofu. Saw that in an earlier post (veg = dairy) and just wanted to correct the misconception on behalf of vegetarians
