I don't know if the friend watching her has kids, has been through the potty training stage with kids or not, etc., but I would definitely talk to her today and explain where you are in the process and that you would not want to put her into diapers or pull-ups at this point; however, I also would listen if that friend sounds hesitant about your child being in her care all day yet unable to use the potty. This friend's doing you a favor, I assume, and if she has other kids around to watch or has to take your daughter with her on errands, etc., it's asking a lot of her to expect her to hover and watch your daughter all day for signs of potty-readiness. If she says, oh, it's fine, we'll be right here at home and I have plenty of time to work with her, then agree with the friend that you can send your little girl to her diaper- and pull-up-less, but be sure the friend is fully on board with that choice.
Frankly, despite the fact I'd usually say don't put a child back into diapers or pull-ups at this point, I would override that in this case with the fact your daughter is staying with someone who is not necessarily buying into helping you potty train. If the friend is balky, you could end up losing a friend, or at least losing that friend's help while you work.
It might be best to go into pull-ups and put off trying again for at least a month; I would not do pull-ups on working days and potty train on days off, because that would confuse your child. I would arrange to potty train at a time when you will be mostly at home with her for at least a week and won't be in the position of a few days of training followed by sending her somewhere she may or may not be able to go in just panties.