Definitely seek a second opinion.

Ask her how she considers a Group IA element potasium to be "heavy metals"?

The term "Heavy Metals" is generally interpreted to include those metals from periodic table groups IIA through VIA. While magnesium and calcium are group IIA metals, they are very early in the group and are almost never classified as "heavy metals". The question begs to be asked that if magnesium is a heavy metal, then what metals are NOT heavy metals? The only metals lighter than magnesium are lithium, berillium and sodium. Lithium and sodium are both IA metals, so the term "heavy metal" becomes rather meaningless if it exclused only one element,

Usually, when the term "Heavy Metals" is used in regard to metal toxicity, it involves metals like lead, arsenic and mercury - metals that are well up on the periodic table - although it can sometimes include boron which is very low in the table.

Get a second opinion.

And, no, you do not sound silly about it all. You sound like someone that is trying to make proper, informed decisions about her health and seeking as much information as you can. Doesn't sound silly to me at all.