Hi Pat - no truth in that at all - tell her to stop worrying.
The mould seams are a feature of pressed glass (which Carnival is, of course). Pretty much all pressed glass has a mould seam or two (or three) on it. Most Carnival bowls, for example, have three mould seams, which can be seen on the exterior of the item.
There's always the exception to the rule - some items such as the Four Flowers Variant plates and bowls, and some of the Crown Crystal Australian items, have no mould seams, because they were made from one piece moulds. It's the exception rather than the norm, though.
There is absolutely no connection at all between the existence of mould seams and value. The things that affect value are scarcity / desirability of pattern, colour and shape - and of course condition as well as overall appearance.
Let's put her mind at rest - the Millersburg Peoples Vase, which recently topped $100,000 at auction, has mould seams. Several in fact :lol: