I suggest running the child support calculator based on the current income and see what the guidelines state is an acceptable amount. If you are paying a fair share of what the guidelines state, then yes you should request that she stay with the original amount. Since she is making more money now, that is what the courts would go by. If child support is set and she is attempting to increase it, I suggest letting her know that her current income is a factor.
If she is purposely taking a job to decrease her income due to child support amount, then it would be a good idea for this to go to court. The courts can be shown that she is leaving a job making more money to increase child support amount. If there is no good reason to decrease her income, such as taking care of the children or her ability to work that job, then the courts can be shown that.
Run the calculator and consult an attorney of your own.