"I am not interested to marry her"- if you are solid and convinced of this stand , then the issue is closed. You need not marry someone you are not interested in. You have to convince your parents with polite firmness.
However if your dislike is only because of " future genetics problems." then I have to say, .well.. there are some ifs and buts. If you do not have opposition to the marriage to your relative girl barring this one point, then you may consider the following parameters and come to a decision:
1. Marrying such a relative is permitted and accepted in the community or sub community you belong to.
2. The girls and her parents do not have any known issues of health problems and are keeping normal health.
3. Your side grandparents and the parents of your brother-in-law also did /do not have any serious health issues which can contribute to hereditary related health issues.
4. Both sides (parents and well wishers from your side and the girl's side) do not have objection to the marriage and actually welcome it.
5. The girls also is ready to marry you.
Then, if all other parameters in selecting a marriage partner are okay for you in this regard, then you may better proceed with this marriage with the relative girl.
The main issue with consanguineous marriages-marriage with close relatives – is that there is one or more common ancestry. In that case the heredity factor probability is more. However if the factors are good then the probability of good is more, and if the factors are not good then that will have more probability. Heredity can influence mental and physical state of a person. However no one can exactly predict about this. Moreover, in the present case, there is one more ancestry which can contribute to heredity- (in this case) the girl's father's side. Even it can take dominance.
Now what is the guarantee that if you marry a non-relative there will not be any health issues? Actually in a marriage with a non-relative, mostly we do not enquire nor get go beyond the boy & girl and to some extent their parents. We do not and cannot conduct detailed enquiries about the health status of the grandparents etc. If the marriage is so-called 'love-marriage', then mostly the knowledge gets limited to the boy and girl only.
Hence on a logical and practical analysis, I will quote that a 'known devil is better than an unknown devil". In your case you know the ancestry and antecedents of your parents, grandparents which means you know a better part of the girl's ancestry also.
So if the 5 points I mentioned above are okay, then you may accept this marriage. Keep faith in the elders' wisdom, keep faith in God ( if you are a believer) that everything will be positive and good.