DEFINITELY tell your friend that you're about to face a financial set-back and that although your husband would love to come, he'll probably need to stay home from the wedding. If she's really a friend she will completely understand your situation, but don't assume that she will KNOW your situation unless you tell her.
When I was first out of college living paycheck to paycheck, I was the maid of honor for a very close girlfriend. She wanted the whole nine yards and I was happy to provide a bridal shower with favors, a bachelorette party, champagne brunch on the wedding day, AND I had to pay for my own dress, shoes, hair and makeup. I did buy her a present from her registry and gave it to her at the shower, but then thought I had spent enough money and didn't buy her another present for the wedding. I didn't think it was an issue but I never told her why and she ended up holding a grudge about it for over a year, which ultimately ended our friendship. It was so ridiculous and it's only with age that I realize I should have just told her up front that I only had so much money to spend. It probably would have changed her expectations about my obligations, and we might still be friends.
And don't let your pride get in the way of letting her help you financially either. It's her wedding and if it matters to her to have both of you there, then it's fine for her (or her father) to help. Just set your personal financial limits (how much you can spend on travel, eating out, a gift etc.) and then focus on how happy your friend will be to have you there.
Oh, and don't forget to think outside the box for ways to save money. Are there friends of hers that could pick you up from the airport and share the drive to the wedding? Is there a family member or friend of her's that you could room with? Just be open about the situation with her, and I'm sure she'll help you think of ways to make it easy.