No, they just chose a table because the restaurant was full. Don't put teachers (or any long-lost acquaintances) in the position of being God-provided and destined to change a person's life. Sorry Una, but if she was regularly in contact with this old teacher it might be different, but to seek her out after a random encounter that had no meaning clearly to the teacher would really feel creepy on the receiving end, particularly knowing she looked up my address, etc.

Look, if the teacher is on FB, maybe just send a friend request and see if she even accepts it to start. Then, if she does, remind her who you are, etc., but don't expect much than a "so nice to hear from you." I'm sorry, but it is intrusive.