This might help you to determine if the loach is pregnant: http://www.loaches.com/species_pages/wloach_spawn.html there isn't a whole lot of info on breeding them. By the way, loaches won't be "pregnant" as they don't carry live young, but she could be carrying eggs.
Have you noticed any other signs of anything from her (marks on the skin/behaviour changes)? Have you checked your water parameters?