I think having diarrhea so bad you end up messing yourself is not very common with IBS, so there's a good chance you won't be as bad off as your mother. Also, having kids weakens a lot of things down there, so your mother may have had control issues due to that. And I don't know how far back into the past your mother's condition was, but it's a lot easier to find restrooms nowadays than, say, the 50's. NOTHING was open on Sundays, so if you were out for a drive, you had no where to go. Heck, when I was a kid in the 80's our Wal-Mart and K-Mart didn't stay open past 6 on a Sunday evening; the town rolled up its sidewalks then, with the exception of food places.
How many calcium pills are you taking? When I was first using them to treat my diarrhea, I was having to take two a day, which is the recommended allowance. I think you can take up to three a day but CHECK with a doctor or pharmacist because you can OD on calcium and mess up your blood or kidneys--can't remember what, but you can only take so much.
I tried the Equalactin back when I was having bad diarrhea, but I don't think it helped me as well as the regular calcium. But I also have an excess bile problem and I wasn't taking my medicine for that condition at the time and I don't think Equalactin works on bile very well. I tried some back when I was in college and was being told that my bad gall bladder was IBS; it didn't prevent my gall bladder attacks, or the ensuing bile, but in between attacks I had very lovely poops; much better than usual since I tended to run a wee bit to the constipated side. If the highest dosage of Caltrate doesn't help you, then you can try the Equalactin and see if that works better. Some people just respond to different kinds of calcium differently.