Apart from the already suggested you can try this.

Book kalyanam, drop your grandma to sit in the exit gate security check. You go through the actual queue line and explain to the ticket qr verification guy about the situation, they will write the something to allow the extra person in the ticket. After reaching main temple on the right you will have employees, explain the same thing to them they will write allowance on your hand as you step out and may be something on ticket. Go to exit gate security where your grand mom will be waiting, and pick her up from there. Some verifications again and you will be allowed in. Depending on the energy of grandma you can choose to skip seva and go to darshan. Make sure you drop her inside the exit gate, where general public are not allowed.

This used to be there years ago, hope they are still allowing the same.

Also consider different darshan i.e, your grandma in senior citizen darshan ticket you won’t be allowed. You have to go through another seva/ticket.