Too many changes will make your CV look bad and give a doubt on to the fact whether person will again jump the ship.
Think of your goals before change of job-Salary is one factor but not the only factor-professional gains in terms of knowledge, new work etc could be important.
Secondly are so many jobs available?
Personally I would not advice frequent job changes.
But then employee has to see his/her objective, long term plans and whether these jumps from job to job are helping her or hindering her.
This is in addition to what Shri Nathrao has said.
If your friend is changing her job every two years then she could be the luckiest person. Getting job in HR is difficult. I have seen HR professionals trying for better opportunity for the years together but in vain. In contrast, if she gets a job without being perceived as job-hopper then it is her good luck.
If your friend has changed her job after every two years and in the interview if she is being asked why she did that then you may tell her that in the interview, she needs to tell the benefits, especially non-financial benefits of the change of her job. Secondly, in what job what she learnt something new or how she could grew because of the change. Lastly if she is able to tell how she could attain her career objectives because of the change of jobs, the better.
HR & Labour Relations Adviser