to answer you topic question. yes he works on maine cows. but to answer you specific no he does not work on maine heifers. or any heifers for that matter. not worth it to breed a charx maine to a show heifer thats on feed.
he will add bone and soundness, but he is usually used to 'feminine up' cattle that are too wide or powerful, your best bet in my mind for sheer power is still milk man or alias. mabey even hooter if you can find semen on him
i think he can work on her regardless. i personally show a steer out of him and a maine x (godfather) cow and i have decided we are going to breed 60% of our a.i cows to him just for the bone and soundness and completeness. he can sire them stout alot of the time as well. dont get me wrong. his dimension is just questionable on a calf if the mama isnt really dimensional
If you bred that heifer to yellow jacket , you better make sure she's at the vet clinic when it's time for her to calve . I've had about 10 born and all of them were 85 lbs +