If you want to chat with a specific person, you can send them an invitation. As soon as they accept the invitation, the chat will show that they have joined. If they decline the invitation, a note will appear instead indicating that they have left the chat.
After a rejection, that person will no longer see an invitation to this chat. Therefore, you cannot invite them again.
To send her a new invitation, you’ll need to delete the start of the chat from your list. Then search for her again and invite her to a new chat.