we know that a cohen may not marry a convert, on account of the fact that she is classed as a ’zonah’. however, if a woman converted, married a yisrael, and then became an ’almonah’, would she then be permitted to marry a kohen?, or do we maintain that once she has become ossurah to a cohen, she will always be ossurah, regardless of her current status. i suppose the same could be asked of a gerusha/chalutsa who remarried and then became an ’almonah’
As you stated, one opinion is that a giyoret may not marry a kohen because of her status as a "zonah". (Rambam Issurei Biah 18) There is also the opinion that the reason a kohen is precluded from a giyoret is because a kohen is restricted to someone who is of Jewish birth.(Yechezkel 44:22 Ravad Issurei Biah 18). Nonetheless, the status of a giyoret to a kohen remains even after an additional marriage.