If there is any illness or defect that could affect married life or it could put one spouse off the other, it must be disclosed and it is haraam to conceal it.
Ibn al-Qayyim (may Allah have mercy on him) said: Every fault which puts the other spouse off, so that the purposes of marriage, namely compassion and love, cannot be achieved, mean that the spouse has the choice of annulling the marriage. (Zaad al-Ma’aad, 5/166)
See also the answer to question no. 111980.
Bedwetting is a fault that the suitor must be told about, but if your sister has recovered, or there is the hope that she will recover soon, then you do not have to inform her suitor.
Shaykh Muhammad ibn Saalih al-‘Uthaymeen (may Allah have mercy on him) was asked: There is a man who proposed marriage to a woman, and it is known that this woman has a physical defect, but this defect is hidden and is not obvious, and there is the hope that this defect may be cured, such as leprosy or vitiligo. Should the suitor be informed of that?
He replied: If a man proposes marriage to a woman who has a hidden defect, that some people know about, if the suitor asks about it, it is obligatory to tell him; this is clear. If he does not ask about it, then he should be told about it, because this comes under the heading of sincere advice, especially if there is no hope of it being corrected or cured. But if there is the hope that it may be corrected or cured, then it is less serious. But there are some things that may be cured, but the process is slow, if indeed it is even possible, such as leprosy, and to the best of my knowledge I don’t think it can be cured completely. Therefore a differentiation should be made between that which may be curable quickly, and that which is curable but will take some time.
End quote from Liqaa’aat al-Baab al-Maftooh@ah, 5/question no. 22
And Allah knows best.