A question about coupling differential signals safely and Input Common Mode Voltage Range
If you have a 'floating battery powered transducer', and you measure 100v between one of its outputs and ground, then you do not have a 'floating' battery powered transducer, you have a transducer which is for some reason 100v above ground.

If you connect that to an amplifier whose permissible common mode input voltage ranges +/-15v about ground, then it certainly would not work linearly, and it would probably get damaged.

If your transducer is truly floating, then it would take only a nominal resistor, say 100k, connected between ground and some terminal on the transducer, say one of the outputs, or a battery terminal, to bring it down to within the amplifier common mode voltage.

If your transducer is elevated to 100v above ground by, say, a connection to the system you are measuring, then you will have to use an amplifier with a larger common mode voltage input. Attenuating both outputs 10:1 with respect to ground will bring them both down to 10v, within your common mode range. You would need to take care to match the two attenuators very carefully, any mismatch will result in some common mode signal appearing incorrectly as differential.