Mom's scared about something all moms are, that is "beware of something I have experienced or learnt from others, or just know that it will hurt you". Do not be disappointed, it is a warning. If the FL wants to do it, she will do it no matter what.
Parenting sometimes get that misunderstanding, that is "saying something that makes your kids misunderstand. If they do something against you they will feel like they have disappointed you". It is a matter of speaking, but this is not a real story and the parents figure here is quite "decisive".
It would have been great that she replied with her feelings, but the author wants to play more with the uneasiness caused by a decision already made.
Hugs for you, it made me feel uncomfortable as well. Let's see how the story develops.(๑•ㅂ•)و✧
I feel like it's because she said what she said that the FL decided to suppress her feelings for ML. I am very disappointed at FL's mom, and I pity the FL. The FL could've had a lot of things much easier in the future if she's honest with the ML, but alas ... (╥﹏╥)