Rash, temp 37.7, cranky and strange vinegar smell

Evening all, 

my little one (3yrs old) has had awful behaviour and been so cranky for a few days, to the point where I wondered yesterday if she's coming down with something. Then, yesterday I noticed a rash on chest and top of stomach, little on neck. Quite faint but def there. Maybe viral rash? Similar to what she had a while back, a week before she came down with a nasty virus. 

Anyway, she has perked up a lot today, v happy and lively. BUT I noticed her pyjamas from last night strangely smelt extremely strongly of vinegar!! V odd. Not sweaty odour, just like neat vinegar.  She was hot when I checked her during night last night and between 37.2 and 37.7c temp today. Still has slight rash. Any ideas? 

Thanks!