For most who are in the Reform movement, the restrictions on those who are Kohanim (singular, a kohain = priest, high priest - the descendants of Aaron), are thought to be irrelevant, and neither the restrictions nor the special status accorded them are followed.
With the complete destruction of the Temple for the second time in the year 70 CE, the focus of Judaism and Jewish practice was transferred from the Temple (a cultic site where offerings for animal sacrifices were the major form of practice, and where the animals were brought, and the rituals were overseen and performed by the kohanim), to a religion that functioned in non-specific locales, using prayer as that which was 'sacrificed', with the primary focus on the home and the observances of the individual/family. This was possible because it had been decreed that Israel shall be 'a nation of priests' - so no need for the kohanim to serve in this ritual fashion absent the ritual in the Temple. More, it was always known that G-d did not need the sacrifices of animals (specifically unlike some religions where one had to feed the gods); this was what people needed to do to express their love and fear of G-d.
Those who are continuing to follow the restrictions on the kohanim do so in the expectation/hope that the Temple will be restored, and that ritual worship through animal sacrifice will again become the norm. This position is roundly rejected by the bulk of those in the Reform movement, who tend to feel that Judaism and Jews have evolved beyond the need for this rather primitive seeming form of worship.
Given that the restriction you mention on marriage of a kohain to a convert (as well as the other restrictions) is related to keeping a kohain 'fit' to serve in the Temple to perform sacrifices, most in the Reform group would not be concerned if you ignored this issue. It is unlikely that the Temple will be restored anytime in your lifetime, if ever, or that Jews will return to animal sacrifice as the form of worship of G-d.
As for her status: here, I would have to say that from what you tell me I cannot determine if this woman was born Jewish or is Jewish. The Reform movement has multiple Responsa (answers to questions) that deal with the status of children of mixed marriages. I will try to summarize them.
A child born to a non-Jewish mother and a non-Jewish father is not Jewish by any definition. To be considered Jewish, that child would have to undergo a conversion.
The typical thinking is that if the mother was Jewish at the time of birth, the child can be considered Jewish. This concept of matirlineality (descent through the mother) is essentially what the Orthodox and Conservative positions follow. The Reform movement also requires that the child be raised in a Jewish home, given a Jewish education, and engage in rituals and public acts that affirm their Jewish status.
The Reform movement has also accepted patrilineality (descent through the father) as a basis for Jewish status. In this instance, a child born to a non-Jewish mother and a Jewish father, where that child is raised in a Jewish home, given a Jewish education, and engages in rituals and public acts that affirm their Jewish status, is accepted as Jewish. This position is not accepted by all movements in the Jewish world - and since this seems likely to be the situation with the woman in whom you are interested, this could be problematic for you and for her down the road.
I would urge you to consult your own rabbi to discuss this situation. You may also find several other answers on the JVO website that relate to your question. I believe that a search for the keyword 'status' may yield most of them.
I wish you happiness.
Rabbi Joe Blair