We are Methodist so the requirements are different but I have a relative on my hubby's side whose wife is Catholic and they are raising their kids in that religion. From what she told me, we've been to all their children's baptisms, at least one Godparent has to be Catholic. Since she wanted her best friend to be the Godmother for the twins, it only worked because BF's hubby is Catholic. For the next child, she wanted someone else who wasn't, so she had her brother stand up as Godfather with her non-Catholic friend as Godmother. She did something similiar with the last two as well. Additionally, they weren't married so that isn't necessary either. So I don't know if both have to be or just one. I do believe it is more about the role they fill than which line she signs on.
Another point would be that if your friend is not Catholic, would she really be the best person to be the Godmother ie responsible for helping raise your daughter in your religion? Or did you intend her to be more the guardian if something happened to you and your husband (ie raise your daughter if necessary)? I ask because in my family, traditionally the two were used as almost one and the same (they were called Godparents but didn't necessarily help with the religious aspect but were intended to be the guardians if something happened to the parents). I hope you know that they are two very different things and if you meant for you friend to fill the guardian role, she can do so without being the Godmother.
Also, is your friend Catholic but maybe just not received her sacraments? If so, is it possible for her to receive them prior to the baptism? Again, I am not familiar w/ the Catholic religion so I am not trying to judge or make assumptions, I just don't know.
For those suggesting she find another denomination...if she is a practicing Catholic, baptism in another religion is not the same as beign baptised in the Catholic religion. Would it solve her dilema of baptism, yes but it would not serve the SAME purpose. When you baptize a child, you are saying you are raising the child in that religion, the godparents are agreeing to help in the journey, and the congregation is also agreeing. To knowingly agree to raise a child in one religion, knowing full well you have no intention of it is lying to God and all involved and asking all involved to do the same.