Q:

but other ladies carried such things, so she also **would have one

Next she selected a parasol from a large and varied assortment in the rear of the store. Not that she had any idea what it was used for; but other ladies carried such things, so she also would have one. 
Source: http://www.classicreader.com/book/2953/1/
I am not sure what "would" means in my sentence. From the context of the paragraph I undestand it that she wants to behave according to the the other ladies. So I would await the form "had to have one".

A:

According to Macmillan Dictionary, definition #1:

would:
used for talking about what was going to happen in the past
a
used for showing what someone expected, intended, promised etc when they were thinking or talking about the future:
James said he would never forgive her.
Most analysts expected that there would be a change in policy.

Consequently, if the context has the reference point in the past, as in your example, we would use would when we were thinking or talking about the future and the sentence reads as:

but other ladies carried such things, so she also would have to carry one.

On the other hand, if we use had to have one as you suggested, the sentence reads:

but other ladies carried such things, so she also had to have one.

To me, both versions imply that she's obliged, bound or under the necessity of carrying one, that is, two different ways of saying the same thing. 

