There are no hard and fast rules for wedding gifts from a bridesmaid. The bridesmaid should simply get the bride a gift which is personal and appropriate.
beau-coup.com has a guide with the etiquette regarding wedding favors. I believe that would be a good place for you to look to get some tips as for what you could put in there!
I would go for a lilac dress and a green hat to match the bridesmaid dresses. But check that matches the colour theme for the wedding
You should be able to find a great deal of do-it-yourself wedding favor ideas from any craft-related website, or craft stores. Try a site like: www.weddingstar.com/DIY-wedding-favors/all
Wedding shops carry Bridesmaid's dresses. If you want to keep the budget low for your wedding then you can rent some lovely Bridesmaid's dresses for your special occasion. 80% of Bridesmaids never wear their dress again, so renting is an option. Although it is your wedding you should take your Bridesmaids with you and be sure the design of the dress suits all of them and let them have a bit of a say in what they think of the dress.
It is really up to the bride. Tradition is that the dress is the same color as the wedding but there have been other colors done.
A jeweler? Most local Jewelers should be able to do custom work.
There is no reason a Muslim bridesmaid cannot be at a Christian wedding. However, it is wise to check with the bridesmaid as to what she should wear in the wedding party if her family is still sticking to their old cultural ways.
It's completely your decision. If you're having a very formal event, favors might be out of place, but otherwise a memento of the occasion would be nice.
The bridesmaid can give the bride a gift on the wedding day. However, sometimes brides will have a bridal shower, and if so, then that is when the present can be given.
I found my wedding favors at a thrift store. They were brand new and only $3. They were enough for about 30 people. Try local thrift stores, and if that doesn't work, try to make some stuff yourself. It would be very unique and creative.
Cheap bridesmaid dresses can be purchased from stores specializing in them, such as Light in the Box. In addition, one can generally repurpose a dress to be suitable for a wedding. One should be able to find reasonably priced dresses from ASOS or Dorothy Perkins.
-spa treatments -bed and breakfast weekend stay -watches (depending on your budget) -matching sunglasses (also depending on your budget)