Can I be denied from being a bus driver because a little girl on the bus was abused by her father and I am a male driver?

You should speak with an attorney that handles discrimination cases. I do not.

Under Federal and Michigan law, an employer cannot discriminate against you on the basis of gender. If the employer refuses to hire you because you are a male, then that refusal could violate federal and/or state law. Based upon the limited facts you have provided, if the girl needs some sort of accommodation due to her past experience, then the employer may be required to accommodate her in a way that does not unlawfully discriminate against you, such as by providing a female aid to accompany the girl on the bus that you drive.

I don't see how it is relevant, but maybe there is more going on with the employer than it is telling you.

I would not think so, the Nexus is simply to remote. The little girl on the bus will eventually have to deal with the fact that half of the human population is male.

Probably not but it depends on the overall situation. Contact an attorney.