Deleting "Hidden" AVG Anti-Virus

My HP 6730b laptop is running Win7 quite happily with AVG, so this is
not my problem, but .....

My sister also has a Laptop (brand/model unknown) that started with Win
7, got on-line updated to Win 8/8.1 and then further on-line updated to
Win 10.

She has BitDefender and Microsoft/Windows standard AV installed and is
generally happy with the operation, however ......

On occasion (every couple of months, maybe), AVG starts up and does a
complete scan which slows her laptop to an almost stop.

She has searched for AVG but can find no listing of it, so has no idea
why it should start up at all.

I'm going to have a play with her Laptop this week-end, so thought I
should ask for suggestions as to what to do. First cab-off-the-rank
would be to have a look in her Control Panel -Programs & Features to
see if I get the option to uninstall AVG from its list. Then I'm
thinking, maybe, get into System to see if AVG is listed there.

Any other suggestions, Please. I've played with Win7 a bit, but I don't
think I've played with 8/8.1/10 systems at all, so any useful advice
gratefully accepted!

--
Daniel