Some studies/experts say that it is better if there are 3 or more years in between babies. Based on my experience with my daughter and grandchildren and friends I suggest that it is to your 1 yo's advantage to be older. She will have you to herself during most of the separation anxiety years and will feel more secure with the new baby. She will also be older and able to understand a bit better about having a new baby sib. She'll definitely be more verbal and can talk about what is happening and how she feels.
I've noticed from questions on this site that having 2 babies close together is very tiring and difficult in many ways. You actually have 2 babies, tho one is a toddler. Toddlers take less work, in some ways, as they get older and can want to be a help as well as actually be a better helper, if one can call it help. lol The advantage is for the older child. (s)he will feel like they're helping which helps some with the adjustment.
Don't count on your little one loving to be around her baby sibling! Being around babies for short periods of time is entirely different than having a baby living with you taking up your parent's time and attention. I've not heard of one family having a smooth adjustment with the older one to the smaller one. Some adjustments are better than others but there are always some difficulties.
Same for being married. It's a change and an adjustment even if the couple of been living together. Attitudes subtly change. I felt this in my marriage, heard other newlyweds express the same feeling and read about this in studies. The first year of marriage is difficult whether or not you've been living together. One article, that I read several years ago, said that for some the adjustment was more difficult as a result of having lived together because couples don't expect that there will be an adjustment period.
I also think it's important for you to have the wedding you want and pregnancy will make that more difficult.
I don't see how you'd be a bad mommy for waiting until later to get pregnant. I also urge you to not have a baby sooner rather than later because your year old wants a baby. A one year old's feelings are so fickle. They are growing and need all the help they can get to mature in a healthy way. They don't need competition from a baby. Your little one will be OK whenever you choose to get pregnant but please make sure you're getting pregnant for your own reasons and not to be a "good" mommy for your little one. Good mommy and bad mommy have absolutely nothing to do with this. Either way you will be a good mommy. I seriously think that you'll have more difficulty being a good mommy with a 2 yo and a 1 yo. It's a whole lot of work! The decision is yours and your fiance's. Do it because you two are ready.