Well of course she’d be troubled by that sudden proposition. Moving in with your partner is a big deal and it’s a big step in a relationship. Obviously a serious matter, a scary thought even, so her response wasn’t surprising - especially, given that, it came out of nowhere.
She’s most likely concerned about several things, such as “flaws” she may have (other than excessive sweating) that she may not want him to witness due to fear of disappointing or scaring him away. She might simply be worried about disagreements that could cause him to lose interest in her and lead to a break up, etc. But I mean that’s the whole point of “dating” and that’s the idea of moving in together. It’s a good way to find out if you’re really compatible with each other before moving forward towards a more serious and even bigger commitment like marriage. But all relationships and situations are not the same, sometimes the timing makes all the difference.