I can't believe I am having to ask for help, since I thought I knew everything there was to know about shedding problems

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However, my baby Sinaloan Milk is having her 3rd problem shed. I even let her swim for about 10 minutes last night in an enclosed small tub with warm water. Fortunately, the skin around her head seems to have sloughed just fine. However, around her body there are places that look stiff and old, you know, like you are SURE this stuff should come off easily.
Last month I put her in a paper lunch bag with a warm, damp washcloth for about 20 minutes. I am about to try mineral oil over her body to see if that helps. It just comes off in pieces.
Now, she is right where all my other snakes are - same temps, same humidity, and I have no other problem shedders.
Are some snakes just like this their whole lives? Have you had problem shedders who grew out of it?
Thanks, again, for the help as always.