What is the ruling and what are the penalties if F6 is using
a first basemans glove to play her position and the offensive
team's coach brings it to your attention in the fourth inning?

Under fed, OK, no penalties.

To expand on that, the requirements of NFHS Rule 1-4-3 apply to everyone except the catcher. So as long as F6's glove meets the requirements of the rule, it's legal, even if designed as a first base glove.

I did a SP game the other day in which the shortstop wore no glove at all. He fielded several ground balls and threw the runners out. He made no errors, though nobody really tested him. We were using a 44 core .375 ball.

I know that in Fed, the fielders must wear a glove. I think in OBR it is not actually required. (I think that in OBR, shoes are not even required by rule.) Couldn't remember whether ASA required a glove or not, so I let the guy play with no glove.