Mother - money vs marriage

So, a little back story first.. I had a child before meeting my FH, he loves my son and treats him as his own. We got engaged and 2 months later I found out I'm pregnant, I had our baby 1 year before the date we picked for our wedding. Because I had a high risk pregnancy we decided to hold off on planning the wedding until after I had the baby. My mother had been very supportive in the beginning, offering to pay for my dress, saying to let her know if I need help with anything (I am trying to do as much DIY as I can), etc. Today I texted my mom saying how the wedding is in 11 months and I don't know where to begin. I was hoping that she would give suggestions or help ease my anxiousness... instead she starts off by saying she doesn't know what to say, that I'll be giving up a lot of money at tax time just for a piece of paper. Now all of a sudden my mother seems to be against me getting married and is trying to talk me out of it just so I continue to get more money back at income tax time. My parents both love my FH so I know it has nothing to do with them not wanting me to marry him for any other reason. I just feel like she is being very negative, insensitive and unsupportive. She keeps saying it's just a piece of paper and not worth losing out on thousands of dollars for it. My mother and I were never close before because of how negative she has always been my entire life. Part of me wants to elope but I know she will be upset she missed the wedding and never let it go. I'm not sure what to do or say, it wouldn't help trying to talk to her about this because she will just get angry and turn it into a fight. I feel like she's ruined some of my excitement about this... is it really that big of a deal? (Taxes) and if so why does anyone get married? I asked her if she regrets getting married and she said no because she didn't have kids before she was married therefore didn't have the option of the money...