Praise be to Allah.
There is nothing wrong with undergoing genetic testing to find out what the problem is and the likelihood of it being passed on to children or causing other problems, because that serves an interest and wards off harm. Taking measures to treat such problems is something that is prescribed in Islamic teaching.
For more information on the permissibility of undergoing testing before marriage, please see the answer to question no. 104675 .
Assuming that a genetic defect is found, it is permissible for this woman to get married, even if there is the possibility of the problem being passed on to her children, on condition that she inform any suitor of her problem.
With regard to her getting married, that is in accordance with the basic principle that marriage is permissible and is encouraged, so as to attain chastity, comfort and love.
As for having children, that is one of the most important objectives of marriage, and it is not ruled out by the possibility of the child being afflicted, for this is something that only Allah knows; the child might be born sound and healthy.
But if it is thought most likely that the child will be born with a deformity, and this is an overwhelming possibility, then the couple may agree not to have children, and they may abort the foetus if it is proven to be deformed, on condition that that be done before the soul is breathed into the fetus, i.e., before the pregnancy reaches one hundred and twenty days.
See the answer to question no. 263741 .
Shaykh Ibn Baaz (may Allah have mercy on him) was asked: I am a Muslim woman, praise be to Allah; I do the obligatory duties that my Lord has enjoined upon me, such as prayer, fasting and zakaah, but I took contraceptive measures during the period when my husband was sick with tuberculosis. This period lasted for approximately ten years, after which my menses ceased completely. Is what I did something that could incur divine wrath? Because my children were afflicted with hemiplegia; some of them died and some of them are still alive, but are afflicted with this disease. Please advise me, may Allah reward you.
If you took contraceptive measures with your husband’s consent, then there is no blame on you. If it was with his consent or agreement, then we hope that there will be no blame on you. But if you did that without his consent or without his knowledge, then you must repent, seek Allah’s forgiveness and regret what you did. And praise be to Allah.
End quote from Fataawa Noor ‘ala ad-Darb (21/421).
It is essential to inform any suitor of this defect, because the scholarly view that is more likely to be correct is that anything that may affect married life or the ability to have children, or that may put one of the spouses off the other, is a defect that must be disclosed.
See the answer to question no. 111980.
If the suitor is aware of the defect, and agrees to go ahead with the marriage, then there is nothing wrong with that, no matter what the problem or disease is.
See the answer to question no. 133329 .
We ask Allah to heal our sister, grant her well-being and bless her with a righteous husband and righteous offspring.
And Allah knows best.