This week on Law & Order: Special Kettle Injury Forensics Unit…
Unless you have the HFE mutation (actually, there are two, possibly three, common mutations in that gene) that leads to hereditary hemochromatosis, your body will only uptake iron if you need it. The proteins that suck iron out of your gut into your bloodstream are controlled by sensor proteins that detect the amount of free iron in your blood. So you can take lots of extra iron and it’ll just pass through you. Being low on iron is a far more common problem than having too much in your system.
Do your mother a favor by taking those pans one day when she’s out, and giving them a really good scrubbing, with detergent and scratching pads, and clean them down to the bare metal for her. She will be astounded at this! 
Joking – Don’t really do this. She will be astounded … and outraged! You will be in your mother’s bad graces for months, and she might even write you out of the will.
I’m with Mangetout.
I use cast iron almost exclusively, have for many years. Keeps the anemia away.
Now that you mention it . . . It’s about iron fortified cereal, not frying pans, but the principle is the same; they add iron or iron compounds to cereal, because the iron is good for you.
The last no doubt a reference to hemochromatosis.
The most recent Countryside magazine had a discussion about cleaning cast iron pans (apparently inspired by a previous suggestion to use oven cleaner :eek: to clean them) and the most popular suggestion was to put the entire pan into a fire and let all of the build-up burn off before you re-season the pan.
Note: Countryside readers do seem to have more open fires going on than yer average American, I think, so this method may not be practical for most people.
It should also be noted that 99.5% of the population don’t have it, and that even for those that do, and even if it’s left untreated, the problems caused by it aren’t actually all that severe. I have it, and I’m probably still more likely to be killed by a skillet falling on my head than by one poisoning me.
All metal pans will leech into food to some degree, and there’s no evidence for any dangers or benefits for most of them (aluminum, copper, etc.), but it is known that for most people, iron cookware has more positive effects than negative. So while it might not be necessary for your mom to use cast iron, it’s certainly not unreasonable.
There’s also the more rare mutations in hemojuvelin (HJV) found in some people of Greek ancestry.
Still, even in the unlikely event of having these disorders, the iron leached from cookware probably pales in comparison to the amount naturally in the food already. It seems like any green-leafy-thing should have loads more iron in it than the pan would lose from cooking, but I’m only making an assumption here.
To season an older pan, once you rub in the oil, bake the pan.
Anyhow… Yeah, my doc tell me to cook my food in a cast iron pan because I don’t eat meat and occasionally get kicked out of the blood donor clinic for low iron. You get small amounts of iron in your food. Just enough for it to be a good thing (barring any medical conditions that have you ODing on iron).
As for the bubbling. My mom has a pan that’s exactly like the one described in the OP. It freaked me out teh first time I was cleaning it and what looked like a chip of iron came off. I’m pretty sure it’s carbon, but damn that stuff is hard and pointy and looks like a mean shard of metal. It used to gross me out when the little flacks ended up on my pancakes. But as an adult, I thoroughly cleaned and re-seasoned her pan and it looks brand new now.
Well, sure. I guess I was just assuming there was a couple decades’ worth of seasoning under the carbon junk, and that a good scrape and rubdown would set it to rights.*
*I know it does, me!
If you have a self cleaning electric oven you can leave the pan in there during the cleaning cycle. The pan then needs to be seasoned again.