Go through border control together?

I'm in the UK on a Tier 4 visa, which is valid until the end of my course (3 more years from now). My niece has been in the UK, staying at home with me. She's taking a short course, which will finish tomorrow. She is a non-visa national, so she applied for a short-term study visa upon arrival (not an entry clearance), and stated in the landing card she'd stay until 10 March. The stamp she was given says "leave to enter...for 6 months", which would reach July 2018. Nothing of this has changed (she's taken the course, and she'll go back to her country on 10 March). We have, however, decided to spend two days in France. By leaving the UK, her visa will elapse, as she does not have an entry clearance, so she'll have to apply for leave to enter again when we return to London (her flight to her home country will leave from Heathrow 2 weeks from now). As she has no more studies to conduct, she'll ask for leave to enter as a standard visitor upon arrival.

As we're uncle and niece, can we go through passport control together when re-entering the UK? I think I could be helpful with English and to explain this whole situation, but I do not know if this would be allowed, as we're travelling back to the UK for different purposes.

Go through together- make sure she has a copy of her return flight details for 10/3