Don't guess!

She won't need to pass immigration, but she will need to follow signs for 'flight connections' (hint: these are purple and unmissable), pass a boarding pass check, then go through security.

60 minutes meets the minimum connecting time (MCT), but only just. This is not a guarantee that she will make it, but that BA reckons that she had a good chance (and they will take the cost if she doesn't).

Impress upon her the importance of being quick, and asking for help if she needs it. Even without speaking, she can wave her boarding card at somebody in uniform and look quizzical.

Flashcards, as armattheus suggested, are also a good idea. Something with her itinerary, booking reference, and phone numbers of relatives would help too.