Not enough current for voltage divider?
Yes, you're on the right track. The values in your voltage divider should be driven mainly by the characteristics of the ADC on the XBee.

Typically, the ADC on a microcontroller requires a source impedance no higher than about 10 k&Omega;. You could use 27 k&Omega; and 12 k&Omega; in your divider; the resulting source impedance would be about 8.3 k&Omega;, well within spec.

The load on the sensor would be 39 k&Omega;, drawing just over 100 &micro;A at 4V.