I think you are being a very thoughtful friend Aveline and I am sure many of us would be wondering what the best thing to do would be. I have to agree with the other posters, though, and offer the invitation. Perhaps hold back for now on asking someone else along, particularly if she doesn’t really know them. That could be saved for another occasion, maybe? I can understand why you think it might be nice to do this, (invite someone else along), but as someone upthread said, maybe your friend might be more comfortable with just you and your DH this time, in case the tears come.
It’s lovely that you are thinking of your friend, so follow your instinct and offer the invitation.