Women's pattern baldness is different.
Men's pattern baldness generally ends up with a "horse shoe" of hair around the sides and back of the head, with the top of the head totally denude of hair.
Not only is the end result fairly common, the path to get there is shared by most men, as well. It usually begins with a gradual recession in the temples.
Then the frontal hairline begins to recede. At the same time, the most forward part of the anterior scalp (mid-scalp) begins to loose hair. This creates the typical "island" of hair that exists between the receding frontal hairline and the middle of the scalp. Somewhere along the way, usually when the anterior scalp begins to lose hair, so too does the crown.
The confluence of the many receding areas leads to a contiguous patch of bald scalp, from the front of the forehead to below the crown. But this is hardly the case with women.
In actuality the term "female pattern baldness" is largely a misnomer, because there is no pattern to female hair loss.

Women's hair loss different patterns, different progressions.
Very few women with hair loss end up with the horse shoe pattern that is the inevitable result of male pattern baldness. Rather, women tend to lose their hair in various combinations of patterns and progressions. Why this is so largely unknown; it is simply a fact that is verifiable by both anecdotal and clinical evidence.

"How can one solution that helps establish a frontal hairline also work for a woman who is suffering diffused hair loss all over the top of her scalp?"

Some women notice their hair loss beginning in the anterior, or mid-scalp region, a few inches behind the hairline. In other women, it is the hairline itself that begins to thin, but there is rarely a true recession as there is with men; rather, the thinning seems to occur randomly throughout the first inch or so of hair without the orderly "march back to the crown" that categorizes most male pattern baldness. As well, very few women experience recession at the temples; most men do.
The wide variety of patterns and progressions in female pattern baldness make a single solution that helps establish a frontal hairline also work for a woman who is suffering diffused hair loss all over the top of her scalp? Quite simply, it can't.
Naturally, there is always the wig, which due to the fact that it covers the entire scalp, means it can theoretically resolve any type or pattern of hair loss. In effect, "one size fits all". However, with this approach the portions of the scalp that are producing hair are also covered, which understandably is less than desirable for most women.
The ideal solution would therefore be for a method to just cosmetically alter the areas where there is hair loss while leaving the areas of the scalp producing hair untouched.
However, there are two problems in taking this approach: the fact and most obvious is that the areas of scalp that are being covered with new hair must flow seamlessly into the uncovered areas that produce growing hair. They have to match almost identically. This is far easier said than done. Not only must the hair match perfectly, but the patterns and density of hair growth must be the same.
The only problem is that in most cases areas of severe thinning are often positioned alongside areas of the scalp that experience more moderate thinning. So even if it were possible for a solution to provide coverage to severely thin areas of moderate thinning would the be prominent. Again, up to now, the solution would be to cover all areas without differentiation in respect to the various degrees of hair loss. That's what a standard wig does. And that's something most women find unappealing.