You can write a letter telling your friend that you would like her to be your platonic plus-one and that you would be honored to have her at the wedding.
<h3>How to write a letter</h3>
Although we cannot write the letter for you, we can give you topics to be developed into a letter. Below you will find the topics about a letter to a friend in which you invite her to your elder brother's wedding.
Begin the letter with "Dear..." and your friend's name.
Ask her how she has been doing and tell her you miss her very much.
Tell her the good news: your elder brother is getting married. You can add some sort of anecdote here to imply that no one thought this day would come.
Ask her to come to the wedding with you. Tell her you can invite a plus-one and the two of you could a platonic date, which means no romantic feelings are involved.
Make sure to let her know that it would be an honor to have her at the wedding with you and that the two of you will have a lot of fun dancing at the party.
Tell her you will be waiting for her reply.
End the letter with "Yours" and your name.
With the information above in mind, a letter can be written inviting your friend to your brother's wedding.
The second sentence shouldn't start with Since because Since is a word to combine sentences like because combines sentences. They are conjunctions I believe.
