@Rammer
There are several things to think about:
First, is the pro domme you are thinking about really know what she is doing with enemas, and specifically a milk & molasses enema?
As I've described elsewhere, there are such persons who claim expertise, but barely know where to put the nozzle. I would opt out if your giver doesn't really know what she's doing. It takes quite some skill and a lot of care to get a colon tube up into someone high enough to work well… that's why I suggested a colon tube size earlier. The colon tube should be inserted between the hard poo and your colon wall. If the tube is simply pushed in, it may well go into the poo or kink and the enema won't work as intended. Too small and it'll curl up, too big and it won't go in between.
Second, don't go trying to ‘enhance’ an M&M enema. They are plenty powerful in and of themselves, as many have written. Also, they are a tried and true enema formula, and have been used for well over 100 years. They are pretty much out of fashion now for a couple of reasons, IMO: when given to relieve severe constipation, the odds are high the result will be a very messy accident for the nurses to clean up, and, the current fashion in very powerful enemas seems to be Lactulose (300ml) and saline (700ml). I suspect that this is because hospital pharmacies have those ingredients in stock, but not milk or molasses. I've had both and they are about equal in effects.
Finally, if you really want to try it, do so. An M&M enema will be a powerful experience, but given by someone who knows what they're doing should not be risky if you're healthy. If the domme doesn't know what to expect and fails to take precautions, she'll soon learn and have a big mess to clean up.