All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
In principle, the guardian is not allowed to reject the fiancé if he is legally competent and the woman under his guardianship wants to marry him. However, if he (i.e. the guardian) fears that she might be afflicted with harm due to her marriage to you while on your condition (i.e. having nerve damage and pain in your vertebrate), then his rejection may be justified. But, if the rejection is based on no valid legal reason, then this would be some sort of preventing the woman from marrying – in which case she has the right to take the issue to the Muslim judge to consider her case and marry her off if it is confirmed with him that her guardian is preventing her for no Islamic reason.
Haashiyatu Ad-Dasooqi from the Maaliki School of jurisprudence reads: “The juristic opinion is that in case the guardian, other than the father, rejects to marry her off to a competent person whom she shows approval for getting married to in the two cases [i.e. whether it is the man who proposes to her, or it is her who wants to get married to the man], then the ruler (or judge) asks him about the reason for this rejection; if he (i.e. the guardian) gives a convincing reason that is viewed reasonable by the ruler, he (i.e. the ruler) returns her to him; otherwise, he would issue an ordinance to him to marry her off. If he still insists on his rejection after the ordinance, then in this case the ruler himself would take the responsibility of marrying her off.” This is on the part of the woman.
As far as you are concerned, you may do your best to convince her guardian to let her marry you. You may seek the intervention of some righteous people to try to convince him. If he is convinced, then praise be to Allah; otherwise, forget about her and look for another woman to marry as there are many women out there.
Allah knows best.