Not sure about avoiding stereotypes. From what I have read and that is as much as I can and from some in depth discussions here (and please read through them) there is no real stereotype.
The things that are constant.
It involves poisoning, but often not what people consider poisoning. Sometimes very clever other times rather stupid but poisoning. Sometimes it is uncovered usually it is not.
ALL MBP mothers are initially admired for their dedication and resilience to adversity in caring for their child.
ALL MBP mothers want attention. Often from someone specific, but sometimes just general spotlight shining on them from above.
ALL MBP mothers thrive in the attention. My mother was never as happy as when she was sitting in the doctors surgery with my brother or calling out a doctor at 11.00pm at night with me near death. I have heard people refer to them as almost glowing at these times, not distraught not tears but totally engaged switched on ... almost glowing.
THINGS THAT VARY
They can be brilliant, mine was very smart or they can be very ordinary. They come from all classes.
The mother can be verbally abusive physically abusive and or emotionally abusive, or a saint.
They can be married or single. Never heard of happily married, but then again with such a sick child who can build the normal relationship with a partner.
One thing I have read is that often have either some medical background or training. That I have found does not play out, so that is the one cliche to avoid.
Munchers are people who know there is nothing wrong with them but always are sick. Hypochondriacs believe they are sick. Munchers know they are not but enjoy playing the doctors. Many MBP mothers are not munchers many are. It varies. Mine was a huge Muncher, and still is.
Hope this helps. Please treat this with the care it deserves. Some victims die, but the ones who don't all have scars. A MBP mother f***s with a child's head. Even if it does not kill them, even if their health rebounds, the focus on them as a medical "thing"rather than a person,the social isolation, lost school, broken family.. no victim comes out okay.