First off tell your Grandmother to go fly a kite in a nice way. You can always say the bigger the better the more to play with!
As for your cakes, they are great. Everyone starts from somewhere.
As for your sister, she asked you to make the cake. She would not have if she did not want you to make the cake.
Now the cake. This is your sister's cake and it will be your gift to her. It will be made with love and that will come through in what you choose to bake for her.
Lighten your heart with this if it helps. What someone else thinks of me is none of my business.
I used to be 254lbs. I lost 100 and I still think the same. As an adult you cannot control what people do and say to you. Nor will you ever know their motives for saying things. But you can control how you react to them. As an adult you have permission to dismiss someone altogether for their opinions.
Evidently, if your grandmother has called you names and now is telling you that you don't have the talent she has an issue. Show her that you do. Everyone at the wedding will be coming to you to congratulate you on what a great job you did for your sister. Then when your grandmother is a witness to this just smile and walk away. She will know better and if she doesn't? There is no way you would change her way of being. Only death will do that and hopefully she will not have the chance to do more damage.

First of all, you are off to a great start with your cakes. It is not easy to get them level and smooth; you have great control on your scroll work, again, not easy to do. As others have said, if your sister did not have faith in your abilities, she would not have asked you to do the cake. The fact that you are her maid of honor shows how important you are to her and how much she loves you and wants you to be an integral part of her day. Focus on that and not the meanness your grandmother has shown. I completely agree with Chiara, you cannot control what others do, but you can control your response. Don't let her see it bothers you, just answer as sweetly as possible "I'm sorry that you feel that way, but _____ (sister's name) doesn't and I plan to be there for her as her maid of honor and as her cake decorator." If she continues, tell her it isn't up for discussion, it is between you and your sister and then walk away or change the subject. My grandmother tends to get resentful and a bit vindictive when she feels left out or things aren't going exactly her way. I think she is lashing out and trying to make us upset because she is. We try to ignore her behavior, if an issue must be addressed, we respectfully let her know that what she said, did, etc. is not going to change things and then change the subject. Sorry that she is making you feel this way. I know that you will make a beautiful cake. Practice the design your sister chose and use your practice time to tailor the design to be exactly what you and your sister want it to be.

Hey there, that is funny what your grandma said, because your situation is simialar to mine. lol My sister wants me to make her wedding cake, and I am scared to death that nobody is going to like it, but after looking for the perfect design and getting a lot of support I am confident that at least the cake will taste good, and the cake will be pretty.... maybe not perfect, but pretty! My mom told me not to do the cake at first, bc people might get sick and blame me that I poisened them lmao.. and she was so serious. Well, I literally just started making cakes in May. I made a cake for my mother in law and my sis liked it and asked me to make hers. I have only made 5 cakes ever, so I have a lot of practice, but I am not scared, bc my sis loves my cakes.... just do the cake, do your best, and don't worry about everyone else, just find the perfect cake and practice! Good Luck!

Definitely keep going and definitely do her cake! Look at it this way- no matter what your grandmother says, your sister has already paid you a very high praise compliment by asking you (trusting you!) to do her wedding cake. The cake you do for her will be done by hands that belong to someone who is filled with love for her- and what better cake can there be than that?

You said that Grandma raised you? Wow. To be raised with that kind of emotional abuse, you are doing awesome where you are at today. Keep it up! You are worthwhile and don't let her tell you differently. You will look great in the wedding, and your cake will too.

Keep us posted!

Repeat after me:

"Lord grant me the serenity to accept the things I cannot change, the courage to change the things that I can and the wisdom to know the difference."

Say this out loud to yourself as often as necessary. I have found enormous strength & self peace by repeating this to myself.

SERENITY: You cannot change other people. Period! All of the begging, pleading, nagging, harassing, crying, screaming, barganing, lectureing in the world will not change someone if they don't want to change themselves.
COURAGE: The only thing in the entire world that you have real control over is yourself. You have the choice to change (if you want to) and you decide what when where & with whom you spend you life with/doing.
WISDOM: Realize what is truely important to you & what is not worth your time, effort or energy. Don't let anything interfere with your happiness. Focus on you & let others worry about their own selves.

Whew! Didn't know that was going to come out of my fingers! I am so sorry that you have negative people involved directly in your life. But you do have the choice wether or not to allow thiem to continue to effect you. Minimize your contact with Grama if that is whats necessary, it may be hard at first, but the longer you are away from her negative vibes, the happier & healthier you will feel. Mental & Emotional abuse are sometime tricky to detect (well, not in this case) and are often hard to wash from your subconcious, but it can be done. And you will be a better person for it.

We love you here no matter what your weight, age, race or degree of decorating. Make your sisters cake! I believe in you!

Lots a love!
Casey

PS Tell Grama where she can stick her piece of wedding cake for me! Oops, was that not nice?!

Thank you guys so much, I went and had a short (and I mean SHORT) visit with my loving grams and when she started on the subject, I declined discussion by saying "My sister and I have decided and that is all that is important here, it is her day." She was upset that I didn't take her advice on dropping out but then again, maybe she is just cranky.... I'm 25 years old, own my own home since I was 17 and have had the same job for over 7 years, think I've done well considering everything that has happened in my life. Maybe she is jealous of the fact it is my little sis and she wasn't raised by her. She always reminds me she is just a 1/2 sister. 1/2 or not we are sisters is what I say. The wedding will be a big hit and I'll be there to help make it one for her..... LOL....