So there is actually two people in question, the first one is my Fiancé's sister. She is older than us, and married. She is really sweet and I like her but we are not super close, but she has made is clear she is going to throw me a bridal shower. She is super sweet and I don't want to hurt her feelings if I don't ask her, but I don't want to put her in an awkward situation by asking her and her not wanting to.
The second one is my brothers girlfriend. She is my age and is very friendly with me. They live together and will most likely be engaged by the time of the wedding. I don't know about asking her either!!
Thank you all for your advice in advance!