Sec 91 cr.p.c.

First come out of the DV unscathed and then think of perjury.If possible get the details of her previous employment from that school if they give.

Let me try and give you a solution . You need to get all facts to fight your case strongly.

1. Get in touch with school to check your wife's employment with them, mostly the school will refuse to disclose the info. However they may disclose verbally the status ....(though that will not help in court of law)
2. Send them email or a letter requesting them to dislcose the said info and also add a note that since there is a legal case and your wife has confirmed that she was working in their school , it is legally required for the school to dislcose the info and (most imp) --- you will issue them a court summons if required  to disclose the said info. The school may or may not reply. If school replies it will reveal true facts  OR say that said info will be disclosed if they receive instructions from legal agencies/police/court.
3. With these email/written letter .....draft an application to court requesting to issue summons to the school as witness to disclose the true facts. 
4. You may also through the court file an application asking your wife to submit proofs of her employment with that school .........she will deny for obvious reasons but which will work in your favour

If your wife has faked the info she will come under pressure. I suggest you do this asap and i dont think there is any particular stage which u can plan and submit this info. You need to expose her lies as early as possible to defend yourself and expose her lies.

PERJURY is not taken seriously by family courts but you can push inconsultation with your lawyer.

Since the DV case is filed after 3 yrs of seperation . On face of it unless she has strong reasons for filing it late the case appears as an Afterthough and with malifide intentions to harass you and family. With the help of a competent lawyer bring this to the notice of the court and explore grounds for rejecting her DV application.

"However, the fact is she never worked for that school." - If she has not worked for that school, how can you prove a negative fact?  As per Evidence Act, negative facts cannot be proved.  So, you deny that fact in your reply and while cross-examining her, you have to ask the pointed question that in which school she was working, how much she was earning and in which bank she was depositing that salary etc. and also seek documents in respect of those facts.  If she,, as averred by you, not worked then her lie would be exposed.   And then only think of perjury etc.

@fighter

Thank you very much for your time and efforts.  You gave very valuable inputs.  I totally agree with your point No. 3 and starting to draft a letter to the concerned school.

Yes, as she has filed the case after 3 years of seperation without any strong reasons therefore we are going with dismissal application under Sec 203 cr.pc.  However, we know that lower courts are most unlikely to dismiss the case.

But, as she has included my old-age parents in it, I dont want to let her go that easily and wish to put a counter blast through perjury.

@Prabhakar

First, thank you for your interest.

As she has already admitted in her petition to have worked there as a salaried employee, therefore my intention is to file application u/s 91 crpc to demand from her (my wife) the copies of Appointment letter and Salary slips.  And obviously she will not have it and in reply she may give some excuses.  Then I will request the court to demand the same documents from the concerned school and in reply the school will submit that no such employee was working with them.

How does it sound??  I am planning to do this before cross.