Query on Indian passport surrender penalty

[aarnags]

Hi,
My wife got British citizenship on 30th Sept 15 and got british passport by 22nd October 15.

There was not enough time or choice left for her to surrender and apply OCI as she had to travel India.
So we thought of using 3 month Grace period (which should be 30th Dec 15).

She went India on 7th Dec 15 on Indian passport and coming back on 7th Jan 15.
I think she has to use Indian passport while coming back to UK at Indian immigration.
Can she show British passport at Indian Immigration for stamp ???

We plan to surrender passport immediately when she come back.
Does her passport attracts any penalty while surrender ???

Please advice.

Thanks in advance.

[geriatrix]

Three month grace period ended on 29-Dec. Using the passport on 7-Jan may attract penalties. If so, it will be at the time of surrender.
I don't think she'll have a visa in her British passport. So, how can she?