M., as others have said, this certainly must be challenging to accept. If your ex is within a reasonable distance from you, perhaps you can make arrangements to have dinner with your daughter during the week (sort of a "girls night out") and perhaps this would take away from the strain on the weekend, plus give you another opportunity to see her. If not, then try to make some time for just the two of you during the weekend w/o 2 year old or new husband.
If your weekends with her now are always around the schedule and routine of your existing family, then this may be disappointing to her since you are her mother....Is she expected to babysit the 2 year old? Does she have to share a room with the new baby? She just may not want to be a part of this "new family" right now... or at least not completely a part of it. This can change over time, so give her some space.
Give your ex a book entitled, "How to successful Father a Daughter" or "How to Father a Successful Daughter" (title is something to that effect). He really needs to know how important his role is into his daughter's self-esteem and consideration of relationships as she gets older. If you ex understands his role, he may then be a good advocate to help strength the relationship of you and your daughter.
Show and tell your daughter how much you respect her. I remember being 13 and not feeling like my parents heard what I had to say. I was old enough to babysit other kids in the neighborhood, but not old enough for my parents to realize that I was growing up and deserving of making some "pre-adult" decision.
Open up the channels of communication without being critical of your daughter, her father or the situation (this does not mean you turn friend instead of parent), it just means you start expressing an awareness of her feelings and actions and ask that she share them so you are better able to make changes or work together to develop reasonable solutions together.
Don't make her feel guilty about staying with her father either...that is where going to my first suggestion of having some separate time with your daughter on a different day may allow for some special experiences and moments that your daughter is craving.