I totally agree that you should change her name and you are definitely not acting like a 2 year old! I grew up in a family where my parents weren’t together and there was a lot of anger between my two families. Being called totally different names by my parents would have made me feel ever more confused, so I think at the least you and her father should agree on a name and both call her by that. It sounds like Madelaina is that name (and it’s a gorgeous name btw) so I think you should change it.
I agree that you should change it and accept that people might not like it but it’s worth it. This won’t be the first time that your parents disagree with your parenting decisions. It can be very hard for parents to accept that their own children are the ones in charge now. Since you “cringe” at the use of [name]Monroe[/name] I wonder if maybe you should just drop it all together. Leaving in as a first middle name is basically giving your family a green light to continue using it.
[name]Plenty[/name] of people change their baby’s name.
I’ve done it. I personally know 3 people who’ve done it. It’s not rare at all.
I agree with everyone, and I’m sorry your family is not being more supportive. If there is anyone who is acting immaturely, it sounds like it is they–they pressured you into choosing a name out of their own anger, and now it sounds like they are taunting you and perhaps attempting to manipulate you rather than taking seriously your regrets; you are actually being quite mature by caring for the father’s feelings as angry as you are at him.
There have been many, many threads about name regret on the forums and quite a few posters have changed their babies’ names. But frankly, I don’t think it matters how many people change their babies’ names–the point is that you cringe at her current name, you have in mind a name that you feels suits her (and that is beautiful, by the way), and this name happens to be the one the father wants for her likewise. I can understand not wanting to displease your family at this time when you want them on your side, but honestly it sounds like they are way overstepping their bounds. Often becoming a mother means establishing new dynamics with our family of origin, and it sounds like perhaps they are resisting this change/your new authority as a mother yourself? I hope you can derive support from the forum (feel free to PM me if you’d like) or from others if you decide to go ahead with a name change. It definitely sounds like you’ve had a rough beginning to motherhood and that you could use some more support–I feel for you!
I have a friend who changed the name of her baby. For about a week or two people thought it a little strange but 6 months on I guarantee you that anyone that matters can see how much she now loves her baby’s name. I feel so happy for her that it was the right decision for her and she had the courage to do it. Now it’s just a quirky little story about the start of her daughter’s life and she now loves telling the story 
[name]Do[/name] what’s in your heart.
I would change it to Madelaina. Madelaina Coryne [name]Monroe[/name] or just Madelaina Coryne would be sweet. I do really like [name]Monroe[/name], but don’t use it just because it’s there. It’s better to love her name and it seems like you love Madelaina.
[name]Emma[/name], at least once a week a mom posts n here that she wants to or has changed her new born’s name, so don’t feel bad about that. It’s ok for u and your babys father to agree on a name, even if that’s the only thing u agree on. Your family are being so immature. I hope it all works out for u.