Friends ...

Did you manage to see the flat? Did you like it ? Did your friend come with you ? You can always ask her to accompany you on your second viewing.

I wouldn't have a problem with getting in touch with her to give her a little reminder. She may be waiting for you to let her know the arrangements. But I would be hurt if I had offered to go with you and you went on your own!
Just realised that this was last Monday so my advice is a little late.
What did you do?

Agree with FF suggestion. A gentle prompt is fine.

Sounds about right FF. The sort of thing I'd do then nobody is under any obligation.

That sounds just right FlexibleFriend no pressure for either party then.

I'd say "the viewing is in an hour if you still want to come with me but no problem if you can't make it. Let me know please."

b1zzle Your friend may have just genuinely forgotten can you text her and tell her you will meet her at the flat if she is available,something may have cropped up over the week-end one never knows.

Do you actually need her opinion? If not, go alone and make your own choice.