Thats what I informed my mum and she told agency too, they said no better to buy and this is for end Nov so almost 2.5months
Travel agents are only looking to increase their business (i.e. sell tickets) even if the situation/the visa process does not demand it. No, it is not necessary to submit tickets for a TRV application
The same travel agents will be happy to quote much higher fare tickets if you want to change the ticket date/sector later if visa processing is delayed.
I suggest you ditch the travel agents. You can get a provisional itinerary - for free, holding the booking for 24 hours - from Expedia or a travel agent who has the Amadeus ticketing software. And mention in the cover letter that you will book confirmed tickets when your mom is issued a TRV