It's not that they never saw anyone go natural, they just never put 2 and 2 together about all those people they saw with nappy hair were also growing locks. It take growing locks to recognize the intermediate steps you see other people going through.
Anyway, Parents have a tendency to think that what you do reflects on them. It doesn't, it reflects on you. Remind her that what you do only effects what people see in you, not her.
My mom is the same. She has hated my locks because they are uneven and nappy. Even after 5 years, she wants me to cut them and go to a salon to have them done "pretty".
Keep letting your hair lock. She can't forcibly cut it. She can make comments and be snippy about them, but if you just talk to her about your reasons, and not cut them off, she might not ever give in, but she might just stop arguing. My mom thought it was a phase. So for years afterwards she wouldn't let me leave the house without comment. But now it's few and far between when she says anything about them. She's pretty much gotten used to my having locks. She's still worried about my finding a job, but she is leaving that up to me.
As for guys with locks wanting girls with hair... That's absurd. I've got locks. My girlfriend doesn't, but that's for her job. Whenever she's got long breaks, I grab a few sections and tnr them for her.
But I digress... Guy's with locks tend to be more earthy and hippieish. They want girls who are pretty earthy and hippieish too. If they have locks, great. If not, then who cares. People generally are attracted to others with similar life views. It doesn't matter what they look like.