You may well find, in this situation, that your colleague is very glad to get rid of the student in question - for all sorts of reasons....
Usually, the more experienced instructors at a school will tend to end up with a 'remedial group' of 'problem' students.
It's nice to get some of these people through, but having done this myself - at a large school with a significant number of airline-sponsored instructors doing two years each - it can get a little fustrating to be one of the senior staff and to fly with most of the difficult cases.
Sometimes, by the way, you simply have to say 'Sorry, but you're not going to make it'. Hard, but fairer than depleting someone's bank account without telling them it's likely to be in vain.