First try being comfortable in your own skin, You do not need to convince anyone, be it your parents ,friends, or strangers of why you are Catholic/ Christian and why you have any faith or any amount of faith in Christ.
Plus if you are certain you want to be married ( which remember that is a sacrament and a vocation with in itself ! ) then your mother an everyone will figure it out eventually when you have someone in your life that is apart of your faith, enriches it, and there wont be any need for such comments, be it serious or joking. Yet there could be this long standing joke of fewwwwww hey my daughters boyfriend you have no clue how lucky ya are i thought she was going to be a nun ha ha ha … so if the comments just never end and they are hurtful to you even though they might not be intended so by your mother, then you need to in your own way get that across with out starting world war 3, I have had to do just that with my dad as i have applied for the religious priesthood / and my dad loves to joke with me, but he also knows he can joke and get under my skin at the same time, so i pretty much have to lay down the law an have had to about three or four times because my dad is very thick headed, and old. An it was hard to do but necessary or else it would have kept going. An mind you I am 34, an my dad is half past older than dirt.
Then I will say if it isn’t your mother challenging your faith, it will always be someone in some shape or form, so keep that in mind too i would suggest.
Finally, consider this, do you not feel any calling to a religious life due to the comments by your mother and her actions towards you, or were you on the fence and thinking about it in some way shape or form and this on goings with your mom has tipped you to not really want to even consider it… Or perhaps your mother sees’ how strong your faith is, and perhaps you exhibit a lot of great qualities that suggests a religious life that you never thought of before… I mean so what if you became a nun like that is something bad ?
an you said you feel that your mom thinks you are weird, I can promise you since you said this here, your mother has no idea how you feel. I am going with the assumption you have a good if not great relationship with your mother, if that is the case talk to her, let her know what is going on with you. If it isn’t a good relationship then just stand strong, be kind and let her know to at least respect you enough to stop with the jokes because you do not find it funny and you take your faith in Christ and the Church seriously. ( kind of said the same thing twice i think but i tend to ramble )