I know a girl who has infantile paralysis. OR: I know a girl who is paralyzed.
Comment:
In constructions with a copula in the relative clause (as here li, with a superficial trace of the French pronoun il, from il est), the copula may superficially look like a resumptive pronoun, but these are better interpreted as strictly verbal. In the plural, for instance, the copula would be ki soon containing no trace of a French pronominal element.