My bridesmaid is pregnant... am i being fair here?

Hi all,


So I have a bit of a dilemma! My fiancé's sister is a bridesmaid in our wedding, and she's recently announced she's pregnant. I'm over the moon for her, especially as she didn't think she would be able to conceive naturally and was planning to start ivf next year.
The dilemma is that as the wedding is now only 12 weeks away, we had already purchased bridesmaids dresses and the dress will not fit her now. As a new dress from the shop we purchased them from would take up to 16 weeks to arrive, buying a new one in a bigger size was not really an option, and making a too small dress bigger through alterations is a challenge that can't always be completed as I'm sure many of you here know.However, I have managed to find what I think will be a solution by ordering her a dress from the same place and in the same colour/material from Ebay which is unused, unaltered and in a larger size. Its not quite the style she initially picked unfortunately, but she says she's not too bothered by that.
I have paid for all of my bridesmaids' dresses (including the new dress from Ebay) and was planning to pay for alterations for them too. As I'd been careful to make sure they all measured properly beforehand, I thought the only alterations that would likely be needed would be the shortening of the hems and then perhaps a few minor tweaks like the waist being taken in a bit or a strap being made a little tighter. I therefore only held back a small-ish budget for the bridesmaids' alterations. She doesn't have any quotes yet, but as the new dress is now going to need to be restructured to accommodate a baby bump and then probably made much smaller for her shoulders and so on, I'm predicting that the alterations she'll need will be way over the budget I've got, especially as I've also paid for a second dress now. I was thinking perhaps as I've paid for the two dresses, I could maybe explain that the budget is tight now (and it is tight!) and kindly ask if she could cover any costs of alterations that are over the budget I already put back had for them? I don't want her to feel she is being punished for being pregnant, but at the same time, I do feel she could perhaps have offered to contribute at least a little to the new dress, as whilst I know it is not her fault really, I'm a bit bummed that I've wasted 120 pounds on the first dress when money is tough as it is and weddings are expensive (can't be returned or exchanged as made to order).
Do you think this is a totally unfair or rude thing to ask? What would you do in my situation?