Marking FIR by person OTHER THAN First Informant ?

In a criminal case, First Informant is unable to depose in Court, as she is sick & bedridden. Judge directed that someone close to First Informant must appear to mark FIR. First Informant is civilian witness, and not official witness. It is heard that successors of official witnesses could mark document on behalf of predeccessors. Similarly, is marking on behalf of another possible in case of civilian witness ? Is FIR marked in this manner valid proof, in the absence of Chief Examination & Cross Examination of original civilian bedridden First Informant ?